Role-playing works best when you know who your character is. Really know him, know him so well that he could be a friend you've had for years... and one way to get off to a flying start is to have a detailed backstory to compliment the necessary game mechanical information that goes on your character sheet. Some games provide a means to create or generate a 'lifepath' that gives you the bare bones of his history prior to game start, some more enlightened GMs require their players to come up with some background, but here's a generic system to provide you with a wealth of detail to add to the basics of character class/profession (and species if applicable) and other basic details that you know from setting him up ready to play.
Mechanically it's quite simple. Get 4d6 of different colours and a d10, roll this handfull once per page, and note the results. Naturally, you may use the rolls as guidance and inspiration rather than taking the results 'as is', but the sheer randomicity can be a spur to your creativity as you take the results and build them into your background.
The areas covered include family structure (are you an only child, etc.), social background, educational background, work history (which may be rolled multiple times for older characters), and personal relationships- if he's married, and how many of the other PCs he already knows (and the nature of their relationships). You'll need to work with the other players to work out the precise details of how they know each other. These tables are followed by a worked example of the system in operation.
Next is a discussion of the concept of a 'character web'. It's a neat way to work out relationships and group dynamics with anyone - PC or NPC alike - with whom your character comes into contact.
Finally there's a neat option for GM use - although the wise GM will be observing and plotting throughout the process, of course! Here it is suggested that the GM make a secret roll for each character in the party. This determines whether that character knows a secret, and the nature of that secret - many of which suggest hidden twists to the relationships that they have with each other. Sit back and watch the paranoia build as you hand out notes to everyone (even if the note contains no secrets whatsoever)!
This is an elegant way to build group dynamics from the outset - a great improvement on the traditional bunch of complete strangers meeting in an inn and deciding to go off risking life and limb in pursuit of loot...er, adventure. The system will work equally well in games of genres other than fantasy too. Well worth a try...