A lot of people think that tighter clothes are for homosexuals, this is NOT true. No woman will assume that you're gay if you're dressed well, and if other guys are making that assumption, it's because you're getting the attention and not them!
This is a good look! (I understand that the model is not that skinny, but the principle applies)
This establishes Rule #1: Do NOT be afraid to wear tight clothing!
There are not a lot of stores that make nice clothes for skinny men, because that is not a terribly large market. These stores make significantly more selling their products to average sized men so it can be difficult to find the right places to shop. HOWEVER, there are also a few stores that specialize in these clothing, and although it can be costly at times, IT. IS. WORTH. IT. Spending $30 on a polo isn't much, and you can find them for that price at the right stores! By far the best store for you to shop at is Express, however, you can look at New York and Company, Guess, and occasionally American Eagle.
This establishes Rule #2: Express is your friend!
As a branch off of Rule #2, we'll talk about what I'm going to call Rule #2.5. I understand that it's not easy to shop in these stores, or to change your fashion dramatically. These stores are expensive, and the people working in them are forced to sell aggressively. Do not let this intimidate you, they are your friend. Yes, they will tell you EVERYTHING looks nice, so take what they say with a grain of salt, bring a friend with you for some advice, and most importantly, shop at the end of season sales. All of these stores have end of season sales when their new lines come out, and you will get these amazing clothes at dirt cheap prices, you can't go wrong.
This establishes Rule #2.5: Do not be afraid to shop in these stores!
The third and final rule is very important. You have to know what looks good, you can't just throw on a bunch of tight clothes and assume that it's going to look great. As a skinny male there are a few points on your upper body that are key. If your clothes are loose or wrinkly there, it will be very noticeable and ruin your look as a whole.
The first thing to know is that Layers are your friend. Wearing a button down shirt is a good look, but with such a prominent bone structure you have to be careful. Especially around the shoulders. Let me explain.
Pay attention closely to this picture:

If you see box #1, you notice that his shoulder line (from his shoulder to his neck) is very smooth, and flat looking (apologizes, hard to describe). This look may be hard to achieve if you're skinny. You'll be able to see both your shoulder at the very tip, and your collar bone, which is not a good look. This can easily be eliminated by layering. If you have a shirt underneath, it can act as sort of a padding, covering up your bone structure, and giving the shirt a perfect fit.
Box #2 is the neck, in this particular models picture, you can see his neck muscles, almost strictly because he has his head turned. This effect is significantly increased in skinny men, however it isn't a huge problem. The problem comes when you have your shirt unbuttoned and you can see your bone structure down to your upper chest. This is ALSO eliminated by layering, go out and buy some Hanes V-Neck under shirts and wash them in hot water, and dry them on a high temperature, they will fit like an XS shirt after two or so washes.
There is a third key spot in your shirt that will make or break your outfit. This part only applies to long sleeved dress shirts, which are a necessity in any well dressed mans attire.
A lot of the problem with being a skinny man is that when you're wearing a dress shirt, it gets incredibly loose around the wrists. If you buy the right clothing, this can be avoided. If it's still a problem, consider rolling both of your sleeves up (NEATLY) to your elbow, you will still look great and this effect will be gone.
Rule 3 is Very Important: Layers are your friend!