Watch the Approach 1: Performance online guitar lesson by Vicki Genfan from Rhythm Makeover: Vicki Genfan
If you’re a more advanced player and/or used to using a down-up strum you can try this pattern that way. I’ve chosen to use all down strokes. Either way, make sure you get a nice solid attack on the bass notes. This gives the riff a bit of a piano sound with nice rhythmic separation between bass notes and upper chord notes.