I look at my bookshelf and pick a name from one of the authors. Sometimes it spawns something else, sometimes Michael Grant will just become Michael Summers. When I think of other things like what they look like, how they'll act, I'll take characteristics from people I know. I'll take one friend's loud mouth and another friend's inquisitive nature and throw them together, see if they work and if they do, slap it on the paper and call it done.
My characters are almost always changing, so at the end I always make sure to go through whatever I've written and make sure who they are at the end is conducive to who they are at the beginning. I tweak their personalities to fit situations, sometimes the other way around. It's about coming up with your own formula and if it comes out how you want it to, great; if it doesn't, change one or two things and see if you like them more now.