I started off learning a few of the basic chords, and just playing 2 over and over again with different strumming patterns, alternating chords (ie G then C then G etc, or D and A, or whatever you want)
Once you manage to nail the chord transitions, you could try strumming differently, or playing 3 chords repeated for example to build up the muscle memory of changing to different chords. Then you could go for 'harder' chords, ie the minors, or suspended ones etc
Maybe you could use a metronome program on the net to keep your timing in check as well? Or use that when playing chords, ie strum a G chord for 4 beats, then a C chord for another 4 beats?