Help! I am never brave enough to pursue the girls I like?

there have been several girls i really like. i even sometimes get signals they like me too, but i always chicken out. like theyll show interest back and ill just shut down (out of nerves) and look away or somethng. i am worried becuase i am missin out on great girls this way, and plus im worried that the way i shy away might look likie im not interested. any tips on how to stay calm and let them know im into them without being tooooo forward?? thanks,