Good evening!
There are a few things to be careful about when editing the "raws."
1. If you don't want to mess up the existing files, you can always make a copy and rename it - just remember to change the file name at the top or it doesn't get parsed...ask me how I know.
2. While tag order doesn't seem to matter, if you want to be able to find stuff later, following the general format of the existing entries is a good idea. Changing a copy of an existing creature or entity is also a good way to be reasonably sure you include all the important parts.
3. Watch your CaSE - some items can be in lower/mixed case, but every tag I can thing of must be [UPPERCASE] if you want it to work.
4. While there's not a LOT of formating, what is there does matter. Watch your [] and : - or, again, things won't work.
5. Use the errorlog.txt file (DF root) after genning and/or embarking to see if stuff is throwing errors. Error messages help you find the broken bits among ALL THOSE LINES.
6. Don't be afraid to stea...borrow ideas from other modders. Find someone who's done something like you want to try and see how they did it. Odds are good they'd be happy to talk to you about your ideas - remembering that you may have more free time than them of course.
7. Have fun dammit! The most amazing stories in DF are usually the spectacular failures. It's not nearly as much fun when everything goes smoothly.
Rochndil, who spends a lot of time breaking stuff before he figures out how it works...