The traditional way to handle it is to have the group find a safe place to
stay and have a puller attack a mob and lead it back to the group.  That way
you have the best chance of dealing with mobs one on one in a relatively
safe environment.  The puller can run up and physically attack the mob, then
run back to camp, but if you have spells available it makes more sense to
use those to aggro the mob from a distance.  "Pulling" works much better
than a helter-skelter "follow the leader" approach, which is what my friends
and I did when we were newbies.  People were always getting lost and the
casters were always running instead of sitting and medding.

Grouping 101: How to make friends and get lotsa lewt.
First thing is to decide if you are a sit at home group, or a roaming group.
sit-at-home's tend to do better, and become the norm after 15-20th.
Basically, the group finds a spot, and everyone with the exception of one
player (the 'puller', who is not necessarily the 'tank' but can be) stays
there, while the puller goes and finds things, gets their attention, and
brings them back to be slaughtered.

There are many many 'roles' in a group, some classes fit strongly in one
niche and no others (Wizard=Non-tanking damage dealer), some do well on the
swing shift (Druids can be damage dealers, healers/buffers, or primitive
crowd control.) Know your role.
Roles:
Puller: You go out and find things for the group to kill. A Puller has to
have the mental ability to navigate, I've grouped with paladins you had to
lead everywhere, but they could tank like noone's business. A puller on the
other hand, can't afford to get lost on his way back to the group. Lost=dead
and could= nasty Corpse Recovery. Classwise, it helps if the puller has ways
to control the number of creatures it's pulling, or if it can pull at a
distance. Crowd control characters can

Tank: You've got time to bleed. It's your job. The 'main tank' is the person
designated to take as much damage as possible from the mobs. I leave a
discussion of the methodology of being a tank to others more qualified. A
tank can also be puller, but in a fast group having a separate puller speeds
things up even more. The classic tanks are Warrior, Shadow Knight, and
Paladin. Other classes can make do in a pinch, and at lower levels the
Ranger, Monk, Beastlord, and Rogue can make do better than most others.

Non-tank damage dealer: Most characters can do this role. You DOT it, nuke
it, beat it with a stick, sic your pet on it, poke it in the back with
pointy things, make it a pin cushion. Once you get into the teens, and
especially the 20s, most classes can no longer stand up to the pounding of a
dark blue con mob, but some can dish out enourmous damage.

Snarer: Druids, rangers, and necromancers (shadowknights too?) can 'snare'
their targets. Lacking those classes, you can get it rooted by others, but
snare is better. At around 25% health many mobs will turn to run. This can
be bad. With snare, they tend to turn to run and not be able to move,
meaning everyone gets to pound the targets for free.

Crowd control: My specialty, crowd control is the art of having the puller
come back with several mobs, and getting all but the one the group is going
to concentrate on out of action for a bit. This can be by charming, mezzing,
rooting, snare/fearing, off tanking with pets or tough tanks, dropping a
spell on them and kiting them around, whatever, but the concept is that the
fight will go better if you can concentrate your firepower as much as
possible on one target at  a time.

Healer: People bleed. Healers make them better. Most healers also 'buff'.

Buffer: Buffers contribute more indirectly to the cause. My enchanter may do
less than 1% of the damage the group does personally, but his haste spells
on the tanks, and mana regen spells on the nukers, mean his effective
contribution probably approaches half the damage the group is doing. The
cleric makes the tank better with his AC/HP buffs. Makes me a better Crowd
controller too, as I can take a few hits now. Most casters have at least a
few buffs. Shamans can load a person down, and are in high demand because of
it.

Debuffer: What buffers do to players, debuffers anti-do to mobs. My
enchanter, along with that nice 70% or so haste, has a 50% or so slow, which
means the mob swings half as often. Snare is technically a debuff but is
important enough to get it's own section above.

Supply sergeant: The mage has a special skill most other classes don't have
in any quantity, the ability to summon lots of odds and ends the group can
find useful. Bandages, arrows, throwing knives, levitation rings, food,
water, vision items, weapons, armor, (good for pets), and caster focus
wear... at high levels a mage can outfit an entire group for that nasty
corpse recovery.  A few other classes get food and drink, and a few
miscellaneous items.
There are other roles, but that gets the major ones I think

For the two classes you listed:
Cleric: Traditional duty: Healer/buffer. Other roles: Nuker, especially
against undead. For all that they wear plate they really cannot tank.
As a low level cleric you will spend most of your time with your rear end on
the ground, medding back that oh so precious mana. What you want to do:
Figure out what are your hp buffs. Those need to be cast on the main tank
(at your low level however, there may not be a well defined tank), and
anyone else that regularly takes hits. If you have the mana available to do
it the good way to do this is to cast it on yourself, then each other
character that is going to get it in turn. Then when yours starts blinking
you know everyone is about to lose their buff.
Pay attention to everyone's hitpoints... When they get low, heal them. Learn
how much of the 'bar' your heals do on each player... it will be different
based on gear and class! Only 'top off' people's health during a lull when
you have full mana.
Mana reports: Sometimes you will get a group, and you will see the tank ask
'Mana?' or 'mr?'. He wants to know the percentage of mana you have
available. Each bubble is 20%, and you can eyeball to about 5%, so report in
10s or 5s (eg /g 70)
Each person has their own style. Some report in bubbles (70% is 3.5), others
actually roleplay it a bit ('meez gotz 3 mugs of sparklies left' for a troll
shaman... that's 3 bubbles)
Another is frequency. I vary. Some groups that grind my mana hard up and
down the bar, I report every time the puller is going out to get more
munchies. Some groups when my mana is just hovering between 40%-80% most of
the time, I'll only warn at 20%.  (actually I usually say /g 20% at 30%, but
that's just my conservative side kicking in) or announce when I'm full mana
(/g fm) so they know we need to kill faster cause they are not pushing me at
all.
(terminology info, some will use /g lom and /g oom for low on mana, out of
mana. For my troll I prefer the more in character 'Me gotz no more
sparklies!')

Paladin: Paladins can be a puller (the lull line helps them there, and stun
pulling gives you a head start back), and are designed to be a tank. With
heavy armor and lots of hitpoints, plus their own buffs and the ability to
heal themselves some, they make good tanks. Learn to love the 'taunt'
button.  Depending on what you are fighting and how things are going, you
may be spot healing yourself, stunning, or just using your mana for pulling.
Lay on hands is your 'fix me now!' key, and  also good when the wizard gets
agro and is folding like wet cardboard. You can be a pocket healer if
necessary, but there are several better alternatives out there. Still it's
better than Mr. Monk can do for others.

Basically in most groups your job will be to go get things for people to
kill, attack targets, try to maintain agro so you bleed the most, and spend
your mana reasonably (If you're not using any of it you're not using your
class to it's fullest.) Note do not just step in and try to take over agro
if you join an existing group with an existing tank. Figure out which one
will be bleeding the most... the other should generally not taunt, though
stunning, etc is useful.

Hope this helps
--
Tyas

   been reading the posts and have heard alot of great suggestions, but i
think (notice i say think, i too am kinda new) that it really depends on the
group.  me and my friend, for example, just go bomb around lavastorm looking
for whatever we can find and then beat the hell out of it.  this works for
me cuz i am a necro and can cast DoT spells and then just meditate while him
and my pet do the rest.  i guess this would be your "roaming" group.
   my other favorite group is with me (necro), a couple of my beastlord
friends, and a cleric.  we all go to the west commonlands and sit by a camp
(i think its called cut throat??? anyway, a camp of all light blues, blues,
and an occasional yellow).  we wait for them to spawn and then we tell
someone to "pull," knowing quite well that its next to impossible to pull
just one and in about 2 seconds we're gonna have about 5 or 6 cut throats
(or is it deathfist?  oh, wait...that's the orcs...) attacking us all at
once, with the occasional young kodak who was just passing by.  ANYWHO...by
the end of the fight we are all out of mana and at about 40% health and
saying things like "damn!" and "close one" or even "that was hella fun!"
after that, we all sit and meditate until we're at full health/mana and the
enemies have respawned.  then go at it again.  (there are quite a few deaths
in this kind of group, but you can still rake in the xp)

so i guess my point is this:
we could sit here for days posting back and forth about different kinds of
groups, but i think the best kind is the kind where you just hook up with
some friends and beat the shiitake mushrooms out of anything that comes your
way.  HAVE FUN!!!

PS
whats the name of that camp in the West Commonlands with the ogres and
barbarians (or are they humans??? i can't tell the difference)

Best thing to do if you are inexperienced in a group is LISTEN.

All but the most obnoxious groups will not have a problem with you
being new to grouping.  They'll generally try to be very helpful.

You are going to make what they perceive as mistakes and they'll tell
you so.  It will be hard at first to judge whether what you are doing
is wrong or whether  it just doesn't fit with their particular play
style.

Take an example:  We've had new people crowding the person calming
mobs.  This often results in mobs getting pulled too early when they
are not all calmed.  If  you listen and stop doing that then fine.  If
you do it on every pull after being asked many times and eventually
cause a serious overpull that wipes the group ... well lets just say
that ain't the way to make friends.