Critical Hit! Picking your Ideal Class in Dungeons and Dragons

How do you pick your class in D’n’D? When I created my first character, I thought about what he would be like first and then picked the race and class backwards. I think because it was my first time playing, I put lots of my heart into my character and as advised by my more learned friends, I made a character that emphasised some of my own traits… Basically… he was a bit of a bastard.¬† But what do you do if you have a blank canvas?