Generally, to get an A you need to study hard.
The only other ways is to be a grinder or if you have a talent in the subject in question. If you're not going to grind (I suggest you don't) and you don't have a special talent, you'll need to study.
You can maximize the study time by studying efficiently. I think the most efficient way to learn is to collaborate with friends about the subject and questions asked in class, but since no one EVER wants to talk about school materials that method is no good.
The second most efficient way is to read before class, listen in class, and then do problems. Why is this so effective? Of course, it needs to be done right which I'll explain in a second. Lots of people do this, but do it all wrong! The first thing is to read the chapter/section before class and make personal efforts to trying to understand what's going on. That is if you don't understand a particular statement, try to re-read it, re-read previous sections that is related to it because a misunderstanding of a previous statement can cause current misunderstandings, search online for other examples if possible, and so. Don't even worry so much about writing notes because it's all there in the textbook and it won't runaway. If anything, you can write notes in the margins for comments that made things click and that way it's in the textbook and it won't runaway! Then go to class the next day or so, and pay attention. Of course, some profs. are not worth paying attention to because they simply write what's in the textbook and you just read that! Otherwise, pay attention and write notes ONLY ON THE EXTRA DETAILS! If the prof. talks about details that already mentionned in the textbook, don't write them down. That is just stupid because you LITERALLY already have those notes and now you're wasting time writing stuff down instead of paying attention. (I think this habit of students is leading profs. to write down textbooks on blackboards because students are really slow at learning because they never go to class semi-prepared and never even think during class.) Now, after you got the IMPORTANT notes ONLY, you can go home that night or the next night and do some problems. The problems will help refresh memory again, but also put the knowledge to work. You can say problems is a way of testing what you learned, but I think that's a bad way to look at it because you technically didn't even learn the material yet so thinking of being tested on something you haven't learned yet is kind of... stupid.
The only time you get tested is when you do an assignment or midterm. They should not be the only source of problems you do. You should do some problems on your own.
Note: I'm a slacker myself, but the above is probably the best combination I've seen. I personally never write notes... ever! I read my textbooks, I answer question and participate in class, I do my own questions and such. I literally never write notes, not even my own. However, I do write notes in the margins now. I'll write notes on exam reviews, but that's really it.