I tell everyone to take an interest in what they are learning. Put it this way, if you love watching Rugby League, you will remember all the rules, all the players etc etc. week in week out, you will know it all. So what i do for modern, eco etc. is to actually take a profound interest in what I am learning, that way it sticks with you more than you would think. This way, you can significantly reduce the amount of study notes you take, but still be able to recall mass amounts of information, purely because you enjoy what you are doing.
Now i realise that many people can't force themselves to enjoy something, but its just something that works really well for me.