Rested bonus gives you a 50% exp boost. The amount increases when you are in a rested state(sanctuary) and logged out, so the longer you stay logged out the longer the boost lasts.
However the amount is % based and a lvl 1 class burns through the rested exp way faster than a higher level class, so it's advisable to expend the rested bonus with your highest level class.
Another exp boost are kill chains. Every time you kill a mob there will be a little timer by your exp bar and if you kill another mob in the given time limit you gain bonus exp for the kill.
This boost continues to increase with every kill but the time frame for killing another mob gets smaller.