Mark is absolutely right, of course. Let me give you the abridged, dead simple way that I learned to do this: Hold a C chord. Now pluck a pattern that has two parts- the first part is Thumb 4th string, then Pinch 5th and 2nd strings. Part two is Thumb 4th, first finger second string, thumb sixth string, then second finger first string. Hum it to yourself- "thumb pinch, thumb-one-thumb-two". Do this 827,000 times and it will hard wire your fingers- then you can begin modifying it with the addition of melody notes, etc. I believe it's best to get a pattern really stuck in your brain, and then learn how to mess with it.