Men often complain that women spend more time thinking about what to wear than they go out; however, women are equally right when they observe that most men seem to put no thought into their appearance at all.
Let's start at the beginning: Ill-fitting clothes have got to go. You might love your baggy sweater or the jeans you haven't really fit into since college, but they send a bad message--that you haven't thought about the way you look--as well as not flattering you the way correctly fitted clothes would. No matter what size you are, there are clothes for you, and you should only buy clothes, especially date clothes, that conform to your shape. When you buy clothes in your size, you'll also notice that you feel more comfortable and hence act more relaxed, which makes you more inherently attractive.
Aside from showering, shaving and having fresh breath (smokers should always carry strong gum or mints), it's important to smell good. However, you should know that "smelling good" isn't necessarily what cologne advertisers want you to think. Men's scents have become bigger and more powerful, in an often quite unattractive way. You shouldn't use cologne as a cover-up for not showering, and there's no excuse for using a cologne that can be sensed from more than 5 feet away. Humans are attracted to the natural smells of a freshly showered body, so a well-selected natural deodorant might just be enough for you.
Finally, basic accessorizing: Keep jewelery to a minimum (unless that's really your thing) and always make sure your belt is the same color as your shoes. Women notice this kind of thing, and it means you care about your public image.
Many men adopt a posture in public, especially if they're nervous, that says that they're unapproachable. Make sure not to cross your arms or cover up your face. Signs of tension are easy to read (Jeanne Segal, PhD) and can make the girl looking at you from the end of the bar stay away, so adopt an easy stance or, if sitting, make sure you're comfortable enough to stay in that position for a while. Drop your shoulders, keep your hands out of your pockets and use your face to give hints. A smile or two never hurts.
Although some think they should travel alone to be most approachable, being in a group is a built-in way for potential mates to see the way you interact with others. When you're comfortable and laughing in a group of friends, you're at your best, so take advantage of these social signals.
Go for What You Want
The type of person we're attracted to is informed by many factors, including television and print media, our friends' expectations and, of course, our own innate desires. You might at times find these definitions of what makes a good mate coming into conflict with each other. Bottom line, you should go for what you're most interested in, because the kind of girl your mother might like to see you with isn't necessarily the one you could build something real with.
This means that, while you're putting your best foot forward, you also have to be honest enough that, if the ball does get rolling and you're start seeing each other, she isn't shocked to discover you don't actually play squash with your investment banker friends on Saturday morning. You can't keep the first-date mask on forever, and when it comes off, the image you present should be very close to what you were putting out in the first place.
Men can take up a lot of room in conversation, either by being loud or by monopolizing time. It's not necessarily intentional, but men often minimize a woman's role as an interlocutor by not giving her the space she needs to discuss her own views. By actively trying to involve a woman in conversation, perhaps by asking her a question and listening to her full answer without interrupting, you show that you're interested in everything she has to offer, and not just that you like her dress.
Balance of Power
You should be comfortable with her making the first move. Everyone from your father to the television has probably told you that men should make the first move, but things are changing, and you should be receptive if she taps your shoulder and would like to buy you a drink.
This idea extends to every aspect of dating and relationships. If she pulls out her credit card, don't ask her to put it away; it is, of course, gentlemanly to offer to pay for your part of a date, but if she has money and wants to spend it on you, you should let her, as a signal that you're equal partners.
Avoid also monopolizing the power in making contact. If you're always the one saying, "I'll call you," you're subtly suggesting that she should not call you. Don't be surprised or offended if she reaches out to you to make a date for Friday night; if you really are equal, either of you should be able to make plans, so long as the other person is willing and free.