Exactly Rachael ... you'll have to listen to the song you're playing ... alot of the current acoustic songs I play are based on a strumming pattern while some are "one strum" and a pause until the next chord is played
Some songs you can do your own pattern to it ... you can play a single chord that is strummed once, pause, wait for the next chord, strum it up-down-up-down, wait for the next chord ... it's all based on strumming patterns ... you'll be able to hear the patterns the more you play ... it's not something picked up right away ...
www.justinguitar.com is a great site to learn strum patterns, that's where I learned mine from and it only took me a few weeks to learn the patterns but they came in very handy ... the more songs I played (especially country songs) the more the strumming patterns became natural to me
Electric: Gibson Les Paul Studio, Schecter Omen 6, PRS SE Custom
Acoustic: Fender Talman, Yamaha
Amp: Fender Super Champ XD/Line6 Spider III 75