And believe me, pretences always show through. If you are not confident, it will be seen through, how much ever you try to hide it. Dress well . It applies to both the sexes. It is NOT macho to be shabbily dressed.
Nothing is a bigger turn off than a pair of dirty jeans, a smelly shirt and a shaggy face.
Though you don't need to look like you have just stepped out of Vogue, you can at least be well dressed. This doesn't necessarily demand a huge wardrobe or a set of designer dresses. Even a pair of jeans and a cotton shirt looks elegant and cool if it is clean and well ironed. Be sure that what you wear suits you. What looks great on your friend need not work for you.