(i) Understand the derivations so that you can derive them yourself or explain them to someone else logically. Just memorising them is not of much value. 
(ii) Modify the assumptions in the derivations to come up with entirely new derivations. Also, try adding more assumptions to standard derivations from the text to derive results for new special cases. 
(iii) Solve lots of problems from the text or other sources. 
(iv) Make up your own problems which are totally new or are modifications of those you solve. Then solve these problems. 
(v) Discuss course material with fellow students and/or senior students.