Exactly, snog his/her face off!Verex said:Actions speak louder than words.
Actually, that works quite well sometimes. It's just a gutsy move if you're unsure how they feel...Just don't lunge at them.
Otherwise, I'd suggest not being too overly-romantic unless there's a high chance they feel the same. If you go paint their name on the White Cliffs of Dover and they never really found you attractive, they could end up being scared or, worse, going out with you out of guilt.
I'd keep it pretty level, get into a situation where you know there's a degree of flirting (curled up watching a film, whatever) and then just say something that shows her how much you mean to her, even if it literally is just saying "You mean a lot to me." Just make sure to say it in the most dramatic way possible; everyone loves cliché.