Endgame Tactics

http://en.lichess.org/QP7QhB43/black#69

Could someone tell me how to draw with pawn down? (R+P vs R)

The rule of thumb is to put your king before the pawn and your rook behind the pawn.

Also, I'm surprised 49... f4 doesn't win!

It sounds like you were in time pressure in any event.

I will forever be amused by this rook endgame:

testurer, there are a lot of rook endgame rules, how to draw or how to win.
its almost impossible to post them all here

testuser*