Here are a few pointers from my experience:
The grouping to gain exp was a very good tip, but let me explain why it is much better than everquest grouping. When you group in AO it seems like the EXP isn't split equally. More like you take a 5-10% hit per teamate to what you would have gotten solo. I solo a monster and I get 230 exp, a group of 5 kill it and I get around 180 exp. How ever it is done mathematically, it deffinitely makes grouping much more enjoyable and rewarding. Here is a trick for the low levels: get a large group of level 2's and have each one soloing his/her own monster (if they can manage to solo). What you will end up having is the majority of the experience from 5-6 kills all at once AKA fast leveling.
Save often! If you die you lose all experience from your last save or the last time you leveled (can't delevel). Save before you enter shops too, because there seems to be zoning problems causing you to get stuck in certain zones - if you get stuck in a shop and you saved before going in you can just /terminate and recover your items from the corpse machine. I am not sure if /terminate will be in the retail product.
From what I saw - The clanners had some great people while omnitek had all the powerlevelers who wanted to make 30 by the end of the beta and pk everyone they saw... At any rate, it seemed like going clan was more fun
Always take easy missions.
Make sure you understand the benefits of a specific race in conjunction with your class before making a comitment to a character.
Bought armor is always better than anything you can get on missions - Armor comes in different types but each type only has 2 differences: look and what it protects. Any armor can be any level (to my understanding). So you could have level 50 leather armor that has massive protection to straight melee but nothing else. So find the armor you want for the protection/look you want and then look for pieces of that armor close to your level/affordability.
Weapons are overrated in the lowlevels but get powerful later on. Try using your hands in the first 5-6 levels but don't rely on martial arts unless you are a martial artist.
Newbie zones are numerous & odd - just because you and your buddy picked clan doesn't mean you both start off right next to each other.
Running may seem useless because you never seem to outrun the monster (except with massive running skill) - but if you are lucky and turn off attack most monsters will give up and just turn around and walk away (even when your at a sliver of health).
Zone lines can be buggy - if you can't zone somewhere keep trying, you most likely arn't on the exact zone line, even though graphically you may be standing in a doorway. Try running side to side.
Rollerrats are always aggresive and will attack on sight, some monsters gang up, some don't. be cautious.