Remind them of what they like
If you have a male friend, who have hinted in the past about what he likes in you - certain physical or emotional characterstics that you possess - learn to highlight those features. Just don't go overboard.
Remember, that when you were friends, how you looked or felt didn't matter because he would love you nonetheless. But, when it comes to love, you need to present yourself in a way that will make him notice.
Change the talk
When people are friends they tend to talk about everything under the sun, from common interests or each other's love interests! If you want this person to relate to you on a more intimate level as well. You could try flirting verbally.
Create the ambience
Instead of going with him to a ususal hangout like a movie or a coffee shop, you could change the venue to a more private and romantic setting.
Change your attitude
If this person is already your friend, he will know how you behave around someone you have more than platonic feelings for. The next time you meet him, start behaving with them the way you would around someone you like.
Body language
This is one of the most powerful tools to hint to people how you feel. The body language that two friends share is very different. All you have to do is change the way you touch your friend and if he has half a brain, he'll get the hint.
All The Best!