Awesome French

What's the most common or best way to tell someone you want them in a sexual way?

Well, in French society, you don’t say it, you make the person understand it by looks and smiles. You invite them to have a drink at your place, you ask them to go in a private place and the person will understand right away. 

Tell such things to someone would make you seem extremely rude, you’ll look like a perving looser. Really, use your best smiles, that’s your best weapon to get laid :D