OK, here is what I would recommend.
For shoes, Clarks are a good decision. Get one brown and one dark gray and, if you can afford it, another pair of brown Dockers-y sort boat shoes (dress shoes last a lot longer if you don't wear them back-to-back; they need to completely dry). These will all be in style far longer than they will last.
If you have a very small budget, go to Target or Old Navy or somewhere like that and get a couple of pair of tan pants and a couple of white or subtly patterned shirts. Use these as your base while you build up the rest. If not, I guess don't.
This is the part that I hate but you might not. A moderately priced shirt or pair of pants that fits properly looks better than a more expensive ill-fitting piece. Go to the local mall and go to all the decent clothing stores (I think J Crew and Banana Republic are good bets, maybe Brooks Brothers, depending on your style and budget; Gap actually has some pretty okay stuff). Try on everything. I hate trying on clothes and looking in mirrors because clothes don't fit me, and it will probably be the case for you, so that's why you just keep looking. Once you find something that looks good, get it and more importantly carefully note what it is.
Find stuff that fits and will work with anything forever -- solid white and blue shirts or subdued and tasteful stripes and patterns. Three white shirts, two blue shirts, and two subtle patterned shirts will go with almost anything. For pants, get two or three flat-front khakis and one or two gray, again depending on your style and budget. As your wardrobe expands you can get more distinctive clothes that you will wear less often. Because stuff is always on sale, I wouldn't expect to pay more than forty bucks or so for a shirt or fifty bucks or more for pants in this range, and you can probably get them for thirty or less if you are willing to really put some legwork into it.
For reference, I am a college history instructor at a laid back school.
H&M and Joseph A Banks and those kind of places (the "Buy one suit, get three free" type) make clothes that are in the long run not worth it because they are cheaply made and won't last long. Don't buy them unless you are in a situation where you've only got a couple of hundred bucks and need a full weeks' worth of clothes.