Well that's difficult to say, everyone is differetn and expresses their feelings in different ways.
I've had a guy barely ever talk to me and just one day add me on MSN and tell me that they are in love with me
I've had a guy flirt around with other girls to get my attention
I've had a guy be really sweet and kind to me and then totally ditch me for someone else
I've had a guy become really shy around me and then gradually become more confortable and ask me out
I've had a guy be a comeplete jerk to me, but it turns out that was his way of expressing his affection
And I've had a guy that I'm friends with just come out and say it one day.
So it really depends on the person.
If I like someone, I usually flirt with them ALOT, ask them to hang out and then tell them.
I don't like keeping my feelings in, I'd rather tell them and get my heart broken than never tell them and keep guessing my whole life.