Well, I will start with Costing.
1.First of all you should know what costing is and why it is necessary (Always remember the best way is introspection, put questions and find answers, you wont forget)
2. You should know what the the various costs associated with a product and its classification.
3. Have good knowledge on cost sheet, like what is the difference between prime cost and works cost, cost of production and cost of goods sold, cost of goods sold and cost of sales.
4. Then take a problem on cost sheet. First read the problem throughly, Next understand what is required (It is the key to open the door), Next think for a min how to solve this, Now start answering, At last check with the answer provided, Write the mistakes you have done and the points which you have to remember in a note book, Keep that note book all the time with you........... and repeat the process.
I want to give you an example in this regard,
If some one asks you to tell about your self, you cant tell perfectly as to what they require
If the same person asks questions like
What is your name?
What are you currently doing?
What about your qualification?
What is your experience?
what are your achievements during your education?
etc., you can answer perfectly. That the difference between simply studying and learning.