Mind-mapping software can be a great way to efficiently write and structure your notes, and has the extra advantage of allowing you to link to internet websites and saved files throughout the mind map. Making mind maps in this way is particularly useful if you're aiming to include dozens of different categories and lots of additional notes which wouldn't fit on a piece of paper. Free mind is a piece of free mind-mapping software available for download which meets all these specifications.
Word association can be particularly useful when constructing mind maps because it helps to assist the natural flow of memory and provide you with pieces of information you might have forgotten to include otherwise. For example, if you're making a mind map about the play Romeo and Juliet, try using word association to expand your existing categories; for instance, a word association of the category "Famous performances" could inspire you to create a new category of "Famous film adaptations."
Don't be afraid to include pieces of information which might seem irrelevant but have some personal meaning. This will enable you to remember the information better, because it's more closely linked to other parts of your memory. With the Romeo and Juliet mind map example, you could write a few notes under each character about who they remind you of in your everyday life; this will reinforce your memory of this character, because you'll remember what they have in common with the people they remind you of each time you remember them. Be creative and write whatever strikes you personally about different information.
Another reason mind maps are so effective is because their very shapes and appearances can be very memorable, enabling you to quickly recall its structure and contents without looking at them. To assist with this, you could decorate the mind map and make each category look different to one another--this way, the shape of each category will look unique, and that uniqueness will bring back information which you might have forgotten otherwise.