You can't overdress
A lot of people under dress for job interviews because they don't want to look stupid. You can never dress up to much for a job interview (this isn't entirely true, don't wear a three piece tux to a gardening job). My general rule of thumb is to dress one level above the job you are going for. There are four main types of jobs. T-shirt and jeans/slacks, shirt and pants, shirt with tie and pants and shirt with tie, coat and pants. So if you are going for a t-shirt job wear a shirt and pants, if you are going for a shirt and pants job put on a tie. If worst comes and to worst and they call you on it "What's with the pants and tie? We wear casual dress here!" Just say you came from somewhere else (I.e, your current job, funeral or wedding.)
