Well first thing I would say, is get in the habit of reading.. I know teachers bang on about.. but this subconscious thing where by reading a lot it automatically helps your writing.. massively.. n i seriously mean this it helps soo much..
it would help if you specify what you are weak at..
which do u need help with.. english literature (studying novels etc) or english language ?
if ur struggling wiv lit.. u need to read first of all..
another thing i find really useful.. is make character profile for each character with the novel ur studying.. also brain storm key themes in the novel and make sure u know well known quotes which you could use as evidence..
hope it helps.. anymore help u need, feel free to ask..