Well, since you're new to the platform, probably the first thing you should do is run software update and download whatever it says is available, particularly the OS, since your iBook may not have the latest version (10.4.4 as of now) preinstalled.
As mentioned previously, most of what you need software-wise comes with your new iBook. One thing it doesn't come with is a good, full-featured word processor. Microsoft Office for the Mac is probably the most popular choice, and there's also the up and coming Pages from Apple, which takes a template-based, page layout drag and drop approach to word processing. Pages also can read and write MS Word files, but if you find yourself interacting mostly with Windows users and Word docs, then Office for the Mac is probably the better choice as it's seamless and care-free with the cross-platform journey.
Insofar as stuff to avoid, I would (and do) avoid any software that modifies or changes the appearance of Apple's applications or any software that modifies or changes the appearance of OS X. It isn't that this stuff doesn't work, most probably do, but they are also almost always problematical when Apple updates the OS (which invariably include updates to the applications that come with it). And Apple updates on a pretty regular basis, so if you want to maintain a clean, well-oiled machine like mine
avoid this stuff. It can cause anything from annoyances to major, mysterious problems going forward.
Along similar lines, one more tip: Don't move, delete, or otherwise tamper with any Apple-installed applications or system files. Don't move Apple applications out of the Applications folder, which is their default location, or for that matter, utility programs located in the Utilities folder. If you want to create your own custom Applications folders (i.e., an Internet Applications folder), you can, but put an alias to the application in the folder instead of moving the actual application. The application alias will look and behave just as if it was the real thing. The reason for this is also for when Apple updates the software. Apple's updater will expect that applications, system files, etc., remain untouched in their default locations as of the last software update. If they are not, bad, bad things can potentially happen.
The bottom line is, you will have much better experience just using your new iBook rather than goofing around with application files or system files. As Apple says, everything "just works" and you can believe it.
