How to prevent losing pawns early on in the game?

How do you prevent losing pawns so early on in the game? I have a hard time with that, and I would like to know some strategies to prevent that. 

Always keep an eye on unprotected pawns and pieces.

I suspect that you're going a point or more down because your opponent is calculating a bit further than you. The other thing which might be happening but probably not so much at your rank, is that they may be playing out a tried and tested opening which is too difficult for you to calculate your way out of. If this is the case then the standard response would be to learn openings, but I think at your current level you should spend your time working on calculating forwards.