Correcting basic attire mistakes
One of the most important investments you can make as a man is having a decent selection of shoes.
Preface: Your age determines your uniform
Choosing clothing is all about context, such as your age, the event, the location, etc. Sure, you can get by in high school in your Converse, Emo boots from the Matrix, or high heels (you wild man!), but once you hit your senior year of college you had better head to DSW and pick up a pair of wingtips. You should really consider a pair of dress shoes even in high school for weddings, funerals, and formal events like graduation. But you will not want a sport coat for cl@sses in high school any more than you would want to see your grandparent in JNCOs.
You don't believe me?
Do you still think sneakers, jeans, and a t-shirt are the outfit of your generation? Open any men's magazine (Esquire, GQ, Maxim, Cargo) and see how many male models are wearing sneakers, jeans, and a t-shirt that are not in an advertisement for jeans. If you need further evidence, visit an engineering school like MIT or Rensselaer and look for the dorkiest kids you can find. I can virtually guarantee they will be wearing tapered jeans, a t-shirt, white sneakers, and white socks. You can also watch the makeover episode of Beauty and the Geek, or any of the Queer Eye for the Straight Guy episodes. 
Above is a Cap Toe and a Wingtip shoe (left to right).
Investing in appearances
You can forget everything they said in school about judging people for who they are, in the real world people judge you based on appearance. If you want a good job or to catch the interest of an attractive woman you need to dress well (then they can get to know you for who you are). You do not need expensive clothes or name brand stuff, but you should think beyond white sneakers and jeans, and stop wearing white socks with black shoes. You can still shop in the clearance section of TJ Maxx and look good.
Why focus first on shoes?
The most overlooked aspect of most men's wardrobes is their footwear. You can get by in jeans and a T-shirt if you have a solid black cap-toe or flat-front casual shoe. If you absolutely must have something sneaker-like, head over to Skechers and look for a hybrid shoe, which combines some of the appearance of a dress shoe with a sneaker.
What you need
You should own a minimum of one pair of sneakers for exercising and lounging around. One pair of casual shoes such as a cap-toe or flat-front shoe is appropriate for going out in the evening, visiting friends and family, and meeting someone casually. Casual shoes can be worn with almost anything, too, such as jeans, khakis, and dress-pants. Wingtips are formal shoes appropriate for weddings, funerals, job interviews, prom, and other important events. However, the wingtip can also be dressed down with jeans and worn with a jacket for a semi-formal event like a cl@ssy dinner. That is three pairs of shoes; not too expensive. Other footwear will be necessary depending on climate (obviously you will want boots in New England and flip-flops in Florida).
Applying theory to reality
Below we have our prototypical geek.
We'll call the first shot O.G., Original Geek. We'll have him untuck his shirt, since you should never tuck a t-shirt shirt into your jeans, particularly without a belt (more on that in future Geek to Chic). Funny how an act as simply as untucking can make someone look better.
Take off the sneakers and put on some casual dress shoes (in this case a flat front shoe from DSW, about $20), and he does look a little better. Not much, though.
We'll keep working on him and make him look a little better in the next Geek to Chic.