First thing I do is look at the CV. If it has been done on a computer but has numerous spelling mistakes (which many do) its obvious they didn't have the intelligence or maybe just couldn't be bothered to spell check or proof read. CV's like that go in the skip.
At the interview, how they are dressed etc. I once had 2 applicants turn up, one in a smart shirt, trousers and tie the other in jeans and tee shirt stinking as though he had just been cleaning out the stable, he even laughed at the other guy for wearing a tie. No need to tell you who got the post.
I find that during the interview it is easy to see who is enthusiastic about the job, a quick check of hobbies will tell you if he has engineering in his blood and a few questions will tell you if he knows anything about how an aircraft works. If you try and bluff/bull**** your way in it will become obvious very quickly, if not at the interview then soon after.