In order to be a good online reader you must do certain things that you might not do when reading a leisurely article or a book. You must first be prepared to read several pages if required and remove all distractions from your environment. First get a good idea of what you are looking for when reading and while you are reading take notes of the main points because you will most likely need this information later on. Try to think about what was read shortly after reading it to better retain the info. There are lots of differences between online reading and normal reading as texts online are generally harder to chronologically graft and retain info because it is mostly all factual and the important things must quickly be isolated from the trivial stuff.
In order to study most efficiently you must study creatively. Try and find what works best for you and use as many useful tools as you can such as helpful websites for studying. Flashcards in google spreadsheets are a very helpful exam studying tool. Study tools work with your brain in a way that they help organize your info to where your brain learns it more naturally by way of dual coding. Use what works best for you but do something more than just memorizing information or you may not retain specific things.