Welcome to what I believe the problem is. I've trained students at airports like this, however, I was trained at a very busy Class Delta airspace. It was for the college, so we often had 10+ aircraft in the airspace at a time yapping away. First flight I was instructed on how to make taxi and takeoff requests.

Hind sight 20/20, I'd have put the radios off for 10 or so lessons to focus on the airplane. Then again, I've been into Boston at 5/6pm (decently busy) and felt completely comfortable except when the guy asked me to sidestep from 22L to 22R. Apparently "22R for seminole 123" doesn't work, you must say cleared in this read back..."cleared for 22R seminole 123."

Ok so enough rambling about my training. Get the book "Say Again, Please" and practice, practice, and more practice. Learn to trim the fat off your replies. Notice the brevity of the example reply above. Another simple example is midfield downwind call, commonly used when doing pattern work in controlled fields:

Wordy: "trenton tower this is cessna 123 at midfield, left, downwind, to land on runway 24"

Restated: "trenton tower cessna 123 left midfield for option" They already know you're on the left side, they assigned it to you. They also know you're landing 24, they assigned you that as well.

Last two tips: Whenever you read back instruction, you don't need to say everything he/she said and you should say your tail number last, not first, as you likely won't forget it and it's typically placarded just in case. Chair flying all this (already mentioned by other poster) is a brilliant idea, but drill it in by getting flight following every flight from here on out, making pilot reports to FSS/Flight Watch, or getting weather reports from them.