What is a general rule for crosswind correction, especially when landing?
What I have learned during my commercial flight training is making use of the speed number.
Take your TAS, devide it by 60. This is your speed number.

Now take you XWC (crosswind component).
Devide the XWC by your speed number. This is the amount of degrees you should crab to stay on track (wind correction angle)

Lets use an example:

We are flying in a C172 at 120kts TAS.
XWC is 18kts from the left. 
120 devided by 60 is 2, so our speed number is 2.
18kts wind devided by 2 is 9. Now adjust your heading by 9 degrees to the left (into the wind), and you should stay on track. 

Worked perfectly fine for me so far.
Hope it helps! Cheers