The thing I've found most effective (but hard to do in practice because it takes time): take very minimal notes, just during lecture / seminar, just enough to r

The thing I've found most effective (but hard to do in practice because it takes time): take very minimal notes, just during lecture / seminar, just enough to remind yourself afterwards what it was about. Try to write more detailed notes afterwards and make all the logical connections the lecturer skipped (there are always some, you can't say everything in 50 or 75 minutes). Then, if there are holes, try to fill them by reading or asking. But that does take a lot of discipline and effort. It's not easy to do for every class you're taking, but sometimes worthwhile.