One of my friends online, Bill Porter, made a library that makes serial communication between 2 Arduino microcontrollers easier. When he first sent me the library to test out for him, I could tell it would be pretty handy and I think it could help some beginners around here. It basically handles the protocol of things for when you are sending a bunch of different information back and forth.
I do not want to copy all of his information he wrote on it over here as that would be redundant. So here is a little scenario of why you might use this:
Say you are sending sensor data from a robot to a controller or base station. You send a light reading value, a distance reading, and a compass reading. Those are 3 different values that you have to distinguish some how from each other. You might try putting an 'L' behind the light reading and a 'D' behind the distance reading or maybe you might use actual NMEA protocol. Basically you are coming up with your own protocol that later you can read in, store, and pick apart.
This library gets rid of the need to do what I said above. Simply send the variable over and recieve it using the same variable name on the other Arduino.
I guess this is not a huge tip, but it is a handy one for beginners trying to do serial communication.