I went for Comp Sci. (B.Sc, two M.Sc. and a PhD). The most important part ist finding your own personal learning type. Theres a distinction between those who learn best listening to lectures, reading textbooks, explaining a topic to others, etc. Start by finding what suits you best.
Here are the things that helped me most (after years of trial and error):
- Going to all appointed lectures and exercises (treating Uni like a job, basically)
- Actually doing the assignments of my Prof gave me
- Avoiding my Laptop/Tablet/Smartphone at Uni. I uses a thin notebook for each lecture and wrote my notes with a pen (more focus on class)
- Using flashcards (I wrote them by hand, but there are software alternatives) for topics, that require a lot of fact memorization
- Making friends with fellow students to help explaining topics to each other and share notes