Linux install comes with a handy little tool called Disk Druid. Its a GUI and it lets you lay out your filesystems with detail.
I strongly recommend that you make the following arrangements, based on my Linux experience.
1) Decide before install what space you need on what filesystem. Its not nearly as much fun making changes after the fact.
2) Swap should be set between 1.5 times and 2.0 times RAM. More will slow you down, less will lead to applications not working correctly.
3) Large /var filesystem. Thats where the logs go, and you need plenty of breathing room there.
4) Define your system purpose. If its learning or play around, any configuration will do. If you want to play with a web server, you need to have that in mind when laying things out. If you want to play with something like Oracle another animal all togetehr.
Most distributions of Linux will set up four primary parititions and the rest will be created in an extended partition.
If there already is an OS, back up the data and blow it away. I don't think dual boot systems are a great idea. Usually too much time is spent in the OS that you know and not enough time is spent learning.
Do's and don'ts
See above.
Don't be afraid to try things.
Don't be afraid to buy a book.
Don't be afraid to post error messages and less broad questions on itrc.
Good start.
SEP
Steven E Protter
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com