Both when I practiced and when I took the real thing, I read each passage through once, at a slightly above average pace, taking notes as I went. I numbered the paragraphs, and gave each paragraph a name (one or two words, strictly for recall purposes). I then wrote down a few key words out of each paragraph that would help jog my memory about where to find facts that I needed. I would then box out each paragraph so that they were visually separated from each other, which makes it easier to find things on the map. Then, once I got to the questions, I could take a glance at the map I made, know exactly which paragraph I needed to look at, and then scroll to it and find the answer.
I earned a 26 RC on the actual DAT using this strategy.
Making a map like this worked great for me, but it doesn't work for everyone. I felt that the key was to practice RC passages up to a point that I felt comfortable with this strategy. Sometimes I would write too much and take too long, sometimes I would write too little and have a hard time going back and finding facts. After about 6-7 practice runs, I had found the right amount for me to write, and I stopped practicing RC altogether at that point (about a month before the test). I think once you've got a sound strategy for this section, your study time will be much higher yield elsewhere.
Another suggestion - FOCUS. When you take the reading comprehension test, more so than any other section, you need to focus. It's easy to spew out biology and chemistry facts that you've learned, but it's another story to take in three passages and answer questions on them with a time limit pushing you. When I got to the reading comprehension section, I told myself that I was going to have laser-sharp focus. I then sat up straight, opened my eyes wide, and payed ridiculously close attention. You know how sometimes you'll be reading a textbook, and all of a sudden you find yourself halfway down the page, and you can't remember a thing you just read? You CANNOT let that happen with the RC section. If you're going to focus during just one hour in your life, make this the hour. 🙂
Then again, I might have just gotten a couple of easy passages on the test.