Tip #1: Watch out for the over use and the vague use of the words ‘theme’ and ‘symbolize.’ Students tend to use the first, not to indicate recurrent ideas that occur in the literary work, but for content, what the work is about. Content: World War 1 traumas. Theme: failure of characters to face reality. ‘Symbolize’ is loosely used by students to represent, to suggest, to be equivalent to, or for just about anything. The term comes from ‘symbol’ so it should be used in that way. In cases of doubt, avoid both.
Tip #2 DETAIL matters. If you make an assertion, argue a point, support it with detail from the text. Looking at a good commentary you will see the constant use of quotation marks, as the smart candidate will be embedding details to support the points s/he makes. Successful candidates do this, and it’s not really very hard to do. On the other hand, just sprinkling quotations throughout your commentary without commenting on why they are there(to support your points) is just as bad. Find a balance.
Tip #3 and maybe the one you are most likely to neglect: PROOFREAD YOUR WORK! That last brilliant point you want to include may not turn out to be as important as leaving time to go back and correct spelling, punctuation and grammar. You’re likely be in a big hurry to get the commentary written, and it’s easy to make a lot of little errors that can reduce your mark in language quite a lot (it’s 1/4 of your whole mark). Leave time and do it!