Be sincere. This is important. Don't take things too lightly,
but don't forget to be human. Telling someone you're interested
should be enjoyable, not frightening.
Be honest. However you decide to tell someone you like them, do it
with the utmost honesty and respect.
Be prepared. Don't shoot from the hip. It's an important step in
the creation of a relationship, so make sure you have some idea
what you want to express and how.
NEVER (BIG NO!) have a friend tell someone for you! You wouldn't
want that special someone thinking you're a mute, now would
you?
good luck 
