Well, I haven't seen any written guides, but you may want to buy a copy of "Linux Security" which is one of the books in the Craig Hunt series. It's pretty good for explaining what kind of things you can do to increase security on your box.
Here are some of the main points...
Remove any packages you're not using or don't plan to use. You don't have to get carried away on this one and start removing everything down to the bare bones. Just get a bunch of the major ones. Type in rpm -qa and it will show you a list of all the rpm's installed on your machine. If you're not sure what something does, type in "rpm -qi package" where "package" is the name of the rpm you're not sure about.
You also need to be sure your packages are always up to date. This is especially true with services that are exposed to the internet. This ensures that people won't be trying to take advantage of some vulnerability that has been just discovered. Get the patch before you become a victim.
Get a good firewall. Nuff said.
The best security is built in layers. Make sure the attacker has a bunch of layers to penetrate before they get to the golden prize... your box. Make it a very difficult challenge so that they will quickly get bored and try somebody else.