1.Their heart starts beating fast
2.Their face changes (shy sometimes)
3.Their caring for you increases
4.Their eyes will be on them at least for 5 sec in 10 sec
But the main thing is that most of the people are afraid to tell what their heart tells them to do.It's never is the persons fault ,the person starts "thinking of the reaction before action" ,which makes them tell nothing and their try will be a total failure.Never try to hide your personality or your true self before him/her, That should be the first thing you should do.Wait for the write time and place to tell.Try to tell what is in your mind in a way that never hurts the feeling of the opposite person.
Hope this tips may work for you people,"NEVER LET IT GO,BEFORE YOU GIVE IT A SHOT............"And "LET, MAY COME WHAT MAY "Because afterwards in future you won't regret that you had a chance and you did not use it to tell something so simple.