I saw a CCENT student ask a pretty common question on a Cisco forum the other day...they wanted to know tips for making all the theory really "stick" when studying.
A great tip in this regard is to practice as much as possible as you study. Get your hands on your home network and investigate as much as possible to drive the theory home.
For example, in the Operation of Data Networks portion of the course, why not download the free protocol analyzer, Wireshark, and start examining the packets that are generated by common network events?
Here is a simulation that I pulled from our course to demonstrate just how valuable this can be. Enjoy: