Pick an easy to type Battle.net account name
If you have a long or difficult to type account name you may find friends and other people are unwiling to send you private messages because it is difficult to type your name. Make it easier on them and yourself by coming up with an easy to type name. Make sure your account name is not offensive so there is no risk it will be reset for violating the Terms of Use Agreement.

Pick a good password
You don't want to lose your account because you have chosen a bad password. Go here for tips on picking a good password.

Follow the rules
You don't want to do something that may get your account disabled or that might get you banned from Battle.net so follow the Terms of Use Agreement that you agreed to when you created your Battle.net account. You never know who might be watching you.

Read the Warnings
The Blizzard Tech Support site has some warnings which you should read.

Learn more about Battle.net!
A nice collection of Battle.net information can be found here.

Use Clan Channels
Create your own Clan Channel. For more information go here.

Use the Friends Commands!
Go here for a list of options.

Learn to Ignore!
You may run into jerks and punks. The best way to deal with them is to ignore them rather than getting into it with them. By responding to them you are only giving them exactly what they are after, attention. Type "/ignore theiraccountname ." There are other options using the friends commands that you can use against them. You can also halt private messages using DND. Learn more about chat commands.

Responding to private messages
Hold down Alt and R on the keyboard to respond to private messages. This will type "/w person'sname " allowing you to quickly respond without typing their name.