Simple advice,start playing a FPS.
When i was playing COD4 (before i change my connection and not being ABLE TO PLAY ONLINE ANYMORE FFS) i was hopping online whenever i felt like it,shoot here,stab there and when i'd have enough i'd stop.
WOW and other similar games don't work this way,they keep you hooked.To play the missions,to lvl,if you have a clan to be around coz they say so.It becomes more like a chore rather a game.Either you stay online for long to become a high-lvler etc or you'll be a low one who's getting his butt handed to him.
I know that recomending a FPS will end up with ppl saying "it's about point of view" but really,pick a game where you can have fun the moment you press the start button.
I say go for it,start playing FPS,lots of fun no matter if you're a beginner or not.