I just took what probably is my last test (university). 
So here is some advice about taking tests.

Create a cheat sheet even you cannot use it during test. 

Keep answers simple and short. 
If you know the test is not time limited, do one exercise after the other.
If you get stuck, move on before frustration. Return later. 

If you know the test's limitation is time: 
rush through and skip what you don't know.
Mark skipped exercises and come back later. 
Last 5 minutes write whatever you know for unsolved exercises.

Derive the needed expression. 
Do not plug in numbers until you have the answer. 
Later check dimensionality and the approximate size of values. 

Eat lightly before test but eat. Bananna. 
Avoid too much fluid, so you do not have to go to the bathroom. 
Go to the bathroom before the test.