A girl who takes care of herself; dresses well; has some self confidence; smiles; and has a decent personality. Sometimes you find all of the above with the exception of a personality -- the girl is hot looking but not worth a single date.
Imo, what makes a girl "hot" is two elements; attitude & actual appearance.
The attitude, pretty much, is confidence in how she looks. This is vital, because w/o this, you cannot be sexy to others. Pretty much, guys can look @ a girl and tell if SHE thinks she looks good. That energy is highly attractive by the way. :)
When it comes to actual appearance, the clothing pretty much shows off her body. Not always in a revealing fashion...pretty much the clothing flatters her body. When it comes to makeup, wear whatever you feel makes you look good...just make sure your makeup doesn't look cake-like. Very unattractive btw.
From a man's point of view, for any woman to be "hot", she HAS to believe that she's hot. All the flattering clothing & makeup in the world cannot compensate for that attitude. I've seen women in sweatpants & a unisex T-shirt that I found sexy...& it wasn't the clothes. It was the way that she carried herself that was intoxicating. :)