There is no "correct" way to play a song. Don't be afraid to experiment with the strumming. There are some basic strumming patterns that are used quite often and fit a lot of situations, that Mike Lynch does a great job in explaining. I'd say those are the straight shuffle, the swing shuffle, the church lick, and the calypso strum. Using those you can pull off most songs, but that doesn't mean it's the only possible way to strum them. Sometimes even changing the character of a song is good.
When learning a new song, I usually start with a straight shuffle (down up down up) until I get a feeling on the chord changes, and then I start playing around with the strumming. There are songs where I don't use a specific strumming pattern, but instead let the strumming flow with how I feel it, and I'm very satisfied with the way they sound that way.