Patching and Plastering - tape and floating help im brain dead

ok so i put up my drywall and i started to put mud on my joints then put me tape on and when i put my cover mud on the joints some times it will cup in some places. What am I doing wrong?
And should you be able to see the tape after you sand it down a little some of my joints look pretty good as i can pull my hand across the joint and its perfectly flat but you can see the tape a litle where i sandit down is this common?
[B]any[B]help would greatly be appreciated thanks diy drywall gods:cool:

As long as the tape is secured well the only thing you need to worry about is smooth level finishing. Tape showing through isn't common but does happen occasionally. I'm not sure I understand what you mean that the mud is cupping - low spots would need more mud - high spots sanded down.

if there are bubbles under the tape then that means you didnt press the tape into the mud enough.did you wet the tape before you put it into the mud?dry paper tape can absorb the water from the mud and cause bubbles so its easier if you have your paper tape in a bucket of water while putting the tape on.just run it thru two fingers to remove excess water and as long as the tape is damp it makes the job much easier. if you can see the tape then that means that you havent put enough mud on the tape or that you are sanding over the joint too much. it takes about three coats to cover tape joints and to make the seam smooth and you need to expand the joint with every coat so that when it is done it should be about a foot wide.