There are a lot of techniques out there for how to absorb information; and, it pains me to say, learning style is somewhat idiosyncratic, and the fundamental concept is to actually learn the material - not just memorize it. So, with those dire portends in mind, here are some strategies I learned from a high school course, reiterated again by almost every college professor I ever had, and other sources.
The Environment and Scheduling a Fake Class
Pick an environment to study in. Whatever is best for you. That you have access to year-round. When you're studying - do it there. The best times to do this are those one or two hours gaps you have between courses. Or, in the morning/evening before/after class. But, pick a time at a regular interval to go to the study environment.
Research does indicate that sleeping after studying is a pretty good rule-of-thumb. Read a lot of information - then go to sleep - let your brain process the stimuli while you're not consciously focusing on it.
Associate Foreign Concepts with Known Concepts
This is a pretty helpful technique as well I picked up along the way. Have you ever been talking with someone who is trying to explain something to you, but you don't really understand and you ask something like, "Is it like when...?" This is what you're doing - building an association from one concept (that you have little or no understanding of) to another (that you have, at least, a decent understanding of).
By building these associations, eventually, learning new concepts will become easier because you will have a larger pool of inter-related concepts instead of various unrelated wading pools with defined edges.
Concepts are More Important than Concretes when Learning
This is one I've picked up recently because I tend to deal with very literal people. So, let's say you're trying to explain the game Cricket to me. As you're explaining I say, "Oh, it's like baseball?" And, you respond with, "No, it's nothing like baseball. It's Cricket...let me start again." It's going to be very difficult for me to wrap my head around what cricket is. But, if we can break the concrete (cricket as a whole) into concepts/abstractions (the components of cricket), then we can get somewhere.
So, "There's a bat, a ball, and bases." "Okay, so it's kind of like baseball in that regard." "Correct. There's even a pitcher like in baseball." Now, I'm starting to build a better conception of what cricket is...then it becomes easier to fit in the details, like the bases are stacked up sticks...
Contamination, Reinforcement, Simmer, Story Time
This was a pretty good break down of the study techniques I used in college (and still use today), during which I had to learn how to use various art media and all the science, math, etc. Unfortunately, the video looks like it's not available anymore, but the wiki is down there for the script - and I will try to summarize. (I've also heard these techniques called other things, such as "saturation" instead of "contamination" and "gestation" instead of "simmer", but the concepts are the same.)
The contamination phase is basically just reading the material. Don't try to remember any of it. You do not consciously care (we are trying to trick the subconscious which remember everything you are exposed to, but your conscious mind can't always dredge it up when you need it). When you hit an interesting point in the reading - just highlight. No worries. No stress. Not a big deal.
The reinforcement phase is basically to write all your notes from lectures and the parts you highlighted in the texts in nice clear handwriting. Again, no pressure to remember any of this stuff. You're just trying to make the "a" that looks like a "0" look like an "a"...you may even find your subconscious helping out when you hit something you scribbled in lecture that looks like "A$@#()" and you think "Huh?" and all the sudden, from somewhere, your mind says, "Oh right! 'ASCII'".
The simmer phase is just that. Don't think about it. Go, watch a movie. Hang out with friends - don't talk about class. Don't talk about your school-related problems. You are neither trying to remember the information nor are you trying to forget the information. It's just not important at the moment - and we hope (and research kinda helps to back up this concept) - when it becomes important/necessary, it will be there.
The story time phase comes from a lot of literature on the subject of learning, which is to teach someone else. Grab a partner in the same class. Sit down, have them ask you questions about the text/lectures (s)he didn't quite understand - you may have an answer. You do the same to him/her. For those areas neither of you have the answer for - look it up. Or, just summarize, out loud, what you read and got from the lectures to this person. (You can do this alone, where you subconscious basically acts as the second person, but I enjoy teaching and learning; so, personally prefer to do this part as "teach someone" kind of thing. And, of course, allow them the opportunity to correct me.)
Type of Learner
Last, but certainly not least, what type of learner are you? There are generally two main spectrums audio-visual and kinetic-passive. If you are an audio learner (gaining more understanding typically from lectures than reading), reading and re-reading probably won't be helpful. So, during your contamination phase, maybe record what you're reading - or simply say it out loud. If you're more kinetic than passive, put the audio tracks into a walkman while you go jogging.
In conclusion, there are a lot of techniques out there for learning how to learn, including many right here at Stack Exchange. But, ultimately, it really comes down to you and what works. You may do best alone; or with a group. You may do best in a quiet environment with little or no distractions; or maybe you're one of those who need music blasting.
As to the question specifically about reading and re-reading - learning occurs when true understanding is achieved. So, only read it as many times as you need to in order to "get it"; for example, you probably don't need to re-read your notes on the answer to 1 + 1...you just "get" it.
As to summaries specifically - by themselves, no technique will just "work" (in that you will retain the information or gain understanding) - learning is a process and a system. I'm a kinetic and visual learner; so, writing summaries never even occurred to me through high school, university, and today. I read something - usually have a pretty decent understanding of it - then run out and talk to others to test my knowledge and understanding (probably one of the reasons I enjoy Stack Exchange). That works for me - will it for you - it depends.
When there is a lot of information to "get" - I have found the techniques above to be very helpful.