Strengths: The monk gains ac faster than any other class for much of the game, and has the special unarmed combat skill which at around mid game does the most damage to a single enemy IF they are in range. Also due to their low equipment needs (and options) they will generally have more item slots open than other classes, which is why they have been called "good pack mules"...
Weaknesses: Very limited range and few ways of gaining any with out severely crippling their damage dealing potential. An example exception is at the start of the game they have one of the best (and most expensive) weapon options until they gain 3+ attacks at level five (which is roughly when unarmed combat should begin). Also, like the other fighter classes of paladin, hunter and warrior, the monk class has no way of dealing group damage for most of the game (at least not yet) which is needed if you don't want to grind to absurdly high levels to get past large groups that can summon or call more into the battle -bandit's cave is the first of these... They also have the lowest hit point gain of all the fighter classes, 8+con bonus vs 16+con bonus. The ac gain rate is not enough to make up for that gap in hp for many situations, such as stun dealing enemies (stun lowers the ac if I recall) and certain magic users and traps (magic by-passes ac and uses sv values instead which the monk has no advantage unless uniquely dwarven vs your other party members).
Because of those unique combinations of strengths and weaknesses a singular monk in a party is best situated in the fourth member slot where he/she can deal their combat strength, or if stunned or otherwise impaired from safety or use in combat, your rear guard/support characters can move up, or your monk, if able, move back as needed. You lose your action including ability to move if stunned for example, so others may need to move forward to get your monk out of danger. In the rear position your monk can recover (with help if necessary) in relative safety. From there, if still in battle, you may: move forward for next round of attacks or to recover your support character, change to ranged weapon (if not already equipped; if it is, attacking then is an option), or as I have used a lot, become healing and supply support...
Filling all those free item slots the monk is likely to have with healing materials appropriate for your level and situation is a good idea to provide support to the rest of your team (and the monk themselves) if ever needed (front or rear). Also if you have bow and arrow, horn or wand users some extra of those may be useful as well, or perhaps a harmonic gem or two, flying carpets etc. In this way your monkly "mule" comes in handy for more than just collecting the junk you may want to sell (or drop if not worth keeping or selling). Obviously trade up non-consumables, or equip/eat food for stat gaining -immediately if in dangerous places or otherwise timely. You can however wait to upgrade stats and equipment in larger batches any time you're in a safe place or grind... Spreading the food around the party is often wise rather than one pig eating it all as I understand it btw...
Save your best runes for the best gloves your monk can wear that you have - because for the monk using unarmed combat it aids when attacking and not just defense that gloves are for all other classes (unless your monk has some other awesome thing to wear on their hands already *wink*). Upgrading the gloves with runes is generally best only when BOTH the gloves and the rune are improved imo - ymmv.
So that's my quick overview for playing a monk in the party based on my experience with the game so far. I hope it expedites some of the learning curve I went through with the monk class for others (and gives a couple other hints along the way for beginners).
Mario has implied in the forums a few neat tweaks to some game elements are in the pipeline so I may update when any of that hits if others don't beat me to it
. In the mean time read some of the other informative posts by smarter and more experienced players, and have fun gaming. 
...Wizardz' walk thrus should be more than enough for most with a bit of patience...
...If none of that helps there are more nefarious ways to gain an edge (with a monk et. al.)... Say 65000 hp, bam-done... But keep game center disabled if you need to resort to hex editing, otherwise you ruin scores for the honest, and it's just weak sauce to do that...
