Hmm...it's been a few months since I did the Net+, and I didn't spend much time preparing for it at all. I only got a 715, but a pass is a pass. I did 6 exams that month, so I wasn't exactly going for high scores.
It seems to me that the biggest things to learn are:
1. TCP/IP and subnetting.
2. Cabling standards (how many pins/wires for different types of cables, the various flavors of copper and fibre, etc).
3. Signaling standards (transmission lengths for various ethernet standards along with wireless standards).
4. Topologies (ring/star/etc).
5. Differences between devices (hub/switch/router/repeater/bridge).
6. Command-line tools (ping, ftp, telnet, etc).
The only that I had a problem with was memorization. I ended up making a cheat-sheet that listed the cabling and signaling standards along with maximum length, transmission speeds, etc organized from fastest to slowest. Then I cram-studied that list while sitting at the parking lot of the exam center. As soon as I got in the exam room I wrote down that list on the eraser board they gave me so I could refer to it.
After you take the exam on your results/scoring page it tells you what categories you missed questions in. It seems to me you would just need to brush up on those areas before testing again.
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CompTIA A+, Network+, Server+, Security+
MCSE:Security 2003
MCTS:Active Directory
MCTS:Network Infrastructure
MCTS:Applications Infrastructure