calm yourself first
bear in mind, you are both humans, you breathe the same air and whatsoever, it's not like the person is a divinity
you are not there to do anything bad, you just want to talk to the person you admire
now...
observe...
think of something you can open up a conversation with
example:
if the person was recently hurt (example: sore thumb, bruised heel (lintos - whatever term you use for that kind of wound) - offer band-aid and ask if he/she is okay
if the person is tired - offer a bottle of water, do it as if it doesn't matter, be casual
if it is at the canteen, just give the person a casual "hi" - if you are classmates open a conversation related to studies
etc....
Remember:
-never act too interested
-never stutter
-blushing is allowed but don't ever act as if you are too shy, do not backdown
-be forward, but never overconfident
finally, remember this well, you can be admired by other people, too. you don't have to hesitate if you want to talk to your crush - sabi nga sa tagalog: amanos lang kayo, tao lang yan, tao ka din.
goodluck!