Unless your date is the girl from "50 First Dates," you never get a second chance to make a first impression. This is why it is so important to dress right for your first date. The good news, especially if you don't have a very expansive wardrobe, is that as long as you don't completely blow it with your choice of outfit, just about any choice of outfit is acceptable.
Note the very important "if" statement in the previous sentence. Choosing poorly can end your first date before it even starts. Never wear any of the following 6 types of clothing to a first date.
1. Dirty Clothing
This one really should go without saying. If you don't have anything clean to wear, you are better off claiming food poisoning and cancelling the date than going in dirty clothing. You should also make sure that the clothing is wrinkle free. If you are good about folding clean clothing, this shouldn't be a problem. If you aren't, learn to iron.
2. Anything with a Controversial Message On It
You know the cardinal rule of dating about not talking about politics or religion on a first date? That applies to clothing, too. Even seemingly friendly messages like the "Coexist" shirt made up of religious symbols could spark a negative reaction in your date. The only message you should be making with your outfit is "I am cool" and maybe "I like cool bands / movies / teams."
3. Something Overly Formal
You've been invited to a picnic at the beach and you show up wearing a button down shirt and dress pants. Hope you took some pictures of your date, because you are never seeing them again. Overdressing for the occasion makes you look pompous. If you aren't a good judge of how to dress, ask your date in advance for some advice.
4. Something Under Formal
You can screw up in either direction when choosing an outfit. If you are eating dinner at a nice restaurant, a collared shirt is almost certainly in order. Thankfully, first dates rarely require any major level of formality, so it is harder to under dress for the occasion than it is to overdress. However, if your first date happens to be a wedding, you darn well better wear a suit.
5. Unnecessarily Revealing Outfits
This is another point that requires a little bit of clarification. Not all revealing outfits are bad. In the beach example above, there is nothing wrong with wearing a bathing suit, even if it is a bikini or a Speedo. However, wearing a thong that leaves practically nothing to the imagination is a bad idea. Similarly, the bathing suit should be replaced or covered up if you decide to go for a walk to a nearby town for something to eat.
This isn't about body shaming or shaming of sexuality. The reason you want to be at least semi-modest is because it allows you to better control the pace of the relationship. Unnecessarily revealing outfits highly suggest that you are interested in progressing sexually in your relationship. Even if that is your goal, until you have felt out your date's interest in that part of your relationship, you are at least as likely to scare away your date as succeed at that goal if you dress in a revealing outfit. Pull that outfit out on the second date if you think that vibe is really there after the first.
6. Anything You Aren't 100% Comfortable In
The last thing you want to be doing during a first date is constantly adjusting your bra or rubbing your feet because your shoes chafe. You know you are uncomfortable because your clothes don't fit right, but your date is likely to believe that something about the date is making you uncomfortable. Even if you explain the situation, it will likely sound like an excuse.
You want to be dressed in something that you pretty much forget is there unless your date happens to be complimenting your outfit. This lets you act naturally and removes one potential bit of awkwardness during the date. Looking at the rules above, this rule trumps all others except for the clean clothes rule. It is better to be dressed slightly less formally than you should than to be fidgeting with your tie all evening, for example.
Finally, comfort applies both to the fit of the outfit and to the style. If you are used to wearing a watch, glasses, or having pants pockets, then don't change any of that up. It looks incredibly awkward if you are constantly checking a bare wrist, attempting to adjust glasses that aren't there, or reaching to the wrong place for your wallet.