if you dont know how or why then dont do it, you have to been on the ball if you do it, like checking plug conditons alot and oil change regularly if your pushing alot of advance
i'd say anything up to 5 degrees advance on top of standard timing is a safe limit for the everyday driver and not having to worry about the engine as long as your change the oil regularly and check on top of engine fluid levels
you will get alot more low down poke by doing that and also gain a bit more poke when overtaking
i'm personnaly running 5 degrees over standard on a 1.2 ecc engine and haven't had any problems as of yet and have a car running 72bhp at the fly, now ive got a wideband a/f ratio gauge i'll be pushing the advance a bit more as i'll know when to stop sooner