Give Safari a chance - it's better than Firefox
Take some time to look through the entirety of the "System Preferences" section when you first get the computer. Gives you a good grounding on what is configurable and will let you use your preferred trackpad/visual/etc behaviour from day one rather than trying to adapt to the defaults.
Learn to use the keyboard shortcuts for window and app management. Things like Command(apple key)+Q to close an application, Command+W to close a window within an application, Command+H to hide an application, etc. It's better to "Hide" an application than to Minimise it on OS X.
Use the "Spotlight" feature (Command+Space) as a quick way to launch applications and find other stuff. You might want to check out an application called Quicksilver as an alternative further down the line.
Make sure you're down with the way applications are installed. You generally download a virtual CD as a .dmg file. You then open this virtual CD and transfer the application from there to the Applications directory on your hard drive. After this, eject the virtual CD and delete it. A lot of people make the mistake of trying to run things directly from the virtual CD.
