There are factors that influence your memory, such as stress and anxiety, injury, distraction, fatigue, and so forth. Those that we can reduce, such as anxiety, will allow your memory to return closer to your baseline. Techniques we use, such as association (anybody else remember "1 lamp post, 2 light switch, 3 stool?") aren't actually improvements to your abilities, because if you had poor ability to recall you would have trouble recalling the initial subject for association.
Verbalizing the information is one technique that I've found is extremely effective. "The red car just drove by me. He didn't indicate when he changed lanes." I used to read my notes out loud, and record them to tape so I could listen to them when I was on the bus, but now I just go to a private space and read the entire text I'm studying out loud. It does get rather difficult with abstractions such as paintings, particularly because I'm unable to form mental pictures, but there are ways I can work within those limitations. Occasionally, people do tend to take the mindset of "Didn't you learn to read without moving your lips?"
Another technique I use is progressive summarizing, which takes quite a while. I would write out sheet after sheet of my notes until I could get it down to a single word or point per topic, and then expand back from that to basically the initial page of my notes again. (This particular technique simply makes use of my wrote learning skills.) It's only really useful for exams where understanding isn't tested.