To simplify the strum, concentrate on using just downstrokes right on the beat. Count out the pulse of the song - 1, 2, 3, 4 - then just add a single downwards strum on each beat.
Don't worry about any of the upstrokes, at least until you are comfortable with this simplified strumming approach.
Make sense? Let me know how it goes.
Mike
Keep rockin!
Mike Olekshy
GT Guitar Coach