The good news is that there are strategies for giving the impression you know everything. This is of particular interest to you as you are coming to a critical period of your life during which you will be tested on nearly everything.
A good way of persuading people that you know a lot is to know details; obscure aspects of a subject. You will find that if you know things that others do not or that few people do then people will presume you know all the obvious stuff.
Make sense?
Good!
Let's say that you will be required to give the impression that you know all the rules of grammar...on an English exam in a few weeks for example. A good way of showing some flair would be to include a correct use of the following rule...
Before a word beginning with a silent h you would use the word 'an' and not 'a'.
For example: I'll be there in an hour
The important thing to remember is that the h should be silent. A common mistake is to get carried away and start going to 'an horrific incident at an hospital'...which sounds an horrible.
I'd suggest you should actively try and show this skill on your exam.
Common words that should be preceded by 'an'
heiress
heir
hour
honest
honour
Post a few sentences practing this rule.
Prizes available for adding apropriate words to the list.