The more you focus the more you remember. So focus is the no.1 important thing to improve your memory.
2. Structure and Organize
It is much easier to acquire and later retrieve a structure and organized data. If you are getting information in a structured way, you are more likely to remember it for longer period of time as compare to the information you will be getting in form of clustered data.
Have you ever noticed that remember and retaining a song is much easier than any context from you books ? The reason is Mnemonics. Though mnemonics you tend to remember things much faster and more accurately. Anything that is comes in a rhyme or tune human are more likely to remember them.
If you connect the new information you are precising with the old one, you will remember both the new and the old one. And its less likely that you forget it.
Trying to make images in your mind, when you see, hear or read something. This way you will be able to memorize things for longer period of time. Also trying to recall them mostly will help you never forget them.