Always use 'su -' instead of 'su'.
Some people have been dealing out this advice like fishes. 'su -' means "use that users environment" which may or may not be what you want. Unless you use the account you're su:ing to often enough that you have it configured exactly how you like it, it's probably not.
Assign user-id 0 to it. (Of all the stupid advice, this is probably the worst.)
DON'T! This will not give root-privileges to the user. It will make the user root, or rather an alias for root. It is not the name "root" that is special. The superuser is the user with user-id 0. And if you're going to run as root all the time (which is a fucking stupid thing to do), just log in as root instead. This way you won't have a "hidden" alias for root lying around. If a normal user needs root-privileges, use sudo(8). If you just need root-privileges temporarily, use su(1).
Add the user to the group disk. Only applicable to ¿debian linux?.
No! The disk user is essentially root. chgrp the cdrom device to cdrom and add the user to that group instead.
kill -9 <pid>
First, try to terminate it with "kill <pid>", to give the process a chance to close log-files, remove lock-files, release resources, and reap child processes properly. If that fails, also try "kill -2 <pid>" and "kill -1 <pid>", THEN use "kill -9 <pid>".
A footnote is in order here as well. If you have a program that forks and dies without daemonizing (daemon(3)) properly, leaving behind living children, the program will show up as a zombie process in ps(1) output. There is no use in trying to kill it. Zombie processes die on their own when their time comes.
Edit /etc/profile and/or /etc/login.defs.
Don't. The current directory is not in root's path for a very good reason: It's a security risk.
It is far too easy for root to browse around the system running commands, only to accidentally run a dangerous program in the current directory, when a system command was intended, whether it's due to a accidental misspelling, or due to an evil user having a rootkit "ls"-lookalike in his home directory, just waiting for root to run it.
Make sure the file is owned by an appropriate user or group, and set permissions for that user or group. Create a new group if necessary.
I haven't yet found one example where 777 are the proper permissions for a file or directory.
("But /tmp and /var/tmp!?" i hear you cry. They have permissions 1777.)
For setting up sound-permissions, see linux sound-permissions.
Login as root and do "rm -rf /"
"rm -rf" will forcibly remove the given directory and all it's subdirectories, which is probably not something you want to do with your root-directory. Instead, consider deleting that huge archive of lesbian porn and "Britney Spears"-mp3s. Other great places to clear out include /tmp and /var/tmp.