Atlantica Online probably has the most extensive ingame tutoring and help systems available in any game that I've played. But even with all that, there are still some tips left to pass on that you won't find so easily in the game. The following is in no particular order with apologies to David Letterman fans.
1) There is no need to beware of strangers bearing gifts. If someone wants to give you a gift of gear or gold, there are no strings attached. AO gives an XP reward based on the gold value of the gift for anyone level 30+ who sends a gift to beginners under level 30. It's totally random who it goes to but thanks are always appreciated.
2) Unless the item is specifically a quest drop, in which case it will have a letter Q on the item icon, you can always buy items needed for quests from the Market. An example is the Basic Training quest from Master Goh which requires you to get him 10 pieces of Rough Leather. Ignore the quest text that says you can get them from the nearby deer. The Market has plenty for you to buy and will save you some time and effort.
3) The Market is what is known as an Auction House in other games. But there is also an Auction in the game as well that functions much like a real auction. Don't get the two confused. If an item says it can't be auctioned, it can still be put on the Market for you to sell.
4) Read your Notes. If the note icon is flashing, chances are you probably want to check out what it has to say. Everything from tips on defeating monsters to email notifications can be found there.
5) Make your Mentor work. If you accept an offer from a player asking to be your Mentor, make sure to put that person through his paces. Mentors receive 200,000 gold upon your reaching level 30. The good ones will have imparted aid in the form of knowledge, monster info, craft info, and even gifts. The really nice ones will give you give you most, if not all, of the 200k to you. If your Mentor is slacking, you can get rid of him from the Mentorship menu.
6) Free League is available at level 1. You can start your climb up the PVP rankings at any time. If you don't mind losing a lot and to higher levels with more mercenaries than you, then FL is a great way to have some fun and earn gold at the same time. The coins you receive from winning and losing can be cashed in right away or held for a rainy day as their value appreciates over time.
7) There are quests that earn you titles and the NPC's that give them out are found outside Athens. More info can be found here. It's best to start working on the titles you are interested in as early as you possibly can.
8) Speaking of which, http://aop.muwing.com/ is a great site in the Wowhead/Allakhazam vein with tons of useful info and utilities about the game. There are also great wikis out there with additional info.
9) Pressing the C key (you might need to try this multiple times) when your mouse is over an item icon will open up the relevant item info giving you details such as what is needed to craft it if it is craftable or which mobs drop them if you have the creature's drop info.
10) You can find out even more tips in this great thread.