Go to any study skills or 'how to' sessions run for freshers, these are often in the library.
Get the OU book called something like, "how to write an essay", it talks you through signposting in an essay, something new to me coming from a science department.
Get the idea you are, "reading for a degree" ie you should be reading every day.
Personal one I find useful.
If I'm writing an essay pick out the main area to study (You can BUG a question even at this level to a certain extent), pick up your text books and a pack of different coloured pot it notes, go to the index in book one and put a post it note on every page that has that subject.
Eg if you are writing about "acquisition of language in children", get pink, yellow and blue post it notes.
Go to the index of the first book, look up 'Aquisition', if the index has this as pages 3 and 12 then go to page 3 and put a pink post it note in - don't read. Then go to p12 and do the same.
Next get the yellow post it notes, look up "language" in the index and put a yellow post it on the pages with "language".
Once you have done this with all your books have a look at the number and colour of notes. A book with lots of post its in all colours is the most relevant so you may want to read the whole book. The book with only one or two only read the one or two paragraphs.
If it is a subject that you may be coming back to then you can leave the post its in the book, just note what each colour is for.
You can also put stars or notes on the post it.
Oh and one very important thing, download some referencing software and store ALL books you reference in it.