The basic principle with strumming is that the strumming hand never stops moving. Even though it might miss, the hand keeps moving. For these patterns, use any chord, open strings (the open chord), or a mute (lightly touch to create a clunk).
Master the motion of down strumming, then move onto 8th note strumming. Realize that you are missing on the way up (hitting only on the downs). When you miss the hand passes across the strings without hitting (or awkardly whipping the hand).
Once you master this (lock it into muscle memory), then learn to miss without altering your strumming motion (like changing speed on a miss, or whipping your hand awkardly to miss).
With this pattern, you are missing a downbeat (and the and of one). Get a feel for the rhythm by tapping on a table. As with all beginner strumming patterns, keep the hand moving. During a rest, you can let the chord ring, or cut it off [hush, choke].
Keep the hand moving over both misses. You can let the chord ring through the and of two and the downbeat of three, or cut it off [hush].