How well , I remember this dilemma , and this is 40 tears down the road . Changing chords and keeping time is a very complex process , both physical and mental . Make sure you can form each chord and make it sound cleanly . I form little triangular patterns and straight line patterns in my head , not this finger here and that finger there ( open d and open A are good examples } . The hard part is that all fingers have to move in unison to change chords and this is where muscle memory comes in , it takes practice , Slowly at first try playing one chord for 4 beats , change chord for 4 beats and so on , gradually change to 2 beats on each chord and finally one beat on each chord all slowly , slowly . It will happen . For rhthym , a metronome or backing track and counting out loud , Again start slow as possible . I suppose I was lucky that my sporting background was rowing , 90 % of training is done at a speed where the boat is just moving and every movement has to be smooth and in sequence with the rest of the crew to keep the boat balanced , Pus you've got that lazy little bum sitting in the back calling the shots and changing the tempo. Keep at it and good luck , it is rewarding in the long run .