Big mik -
Start by getting the C chord. Take as long as you need to, but get it to ring cleanly on every string (except the low E of course, because that's not part of the chord). Now, let go of the guitar neck. Form the open C again, taking as long as you like. Let go. Form the open C again, taking as long as you like. Do that 100 times a night for a few nights.
Once you can get to the C chord reliably taking as long as you like, start getting there from the G chord. Again, take as long as you like. Strum the G, then the C, then the G, then the C. Don't worry about timing yet. Take as long as you like to form each one - but get it clean. Do that 100 times a night for a few nights, until you can do it pretty well.
When you can get the G and C pretty well, and do it cleanly, then start to worry about timing. If you have a metronome, set it. Do four down strums on the G, switch to the C and do four strums, and back to the G and do four strums, and back the C and do four strums, and continue to do this until it makes you sick. Get clean sound. Slow down the metronome as slow as you have to to be able to do this transition with a good clean sound. When you can do it cleanly most of the time (you'll still make blunders), then speed up the metronome a little bit. Keep speeding it up a little at a time until you can transition between the chords at the speed you need to for playing whatever song it is you have in mind.
You can do this with any combination of chords, any pattern. Metronomes are your friend. They just feel like your enemy.
Good luck. We've all been through this. Stick to it and you won't regret it. C is the first booger of a chord, then D, and then barre chords, and then B remains evil forever and always (despite some mutants who seem to be able to throw a B chord or variant at will). It won't be long before you're knocking out C and D and minors and sevenths and whatnot and you'll think back and wonder to yourself how it was ever a problem. It could take weeks, months, or even longer depending on how much time you can dedicate to practice and how fast your finger muscles learn the shapes and get the strength and toughness they need.
- Zurf
Granted B chord amnesty by King of the Mutants (Long live the king).
If it comes from the heart and you add a few beers... it'll be awesome! - Mekidsmom
When in doubt ... hats. - B.G. Dude