I agree with the post above. You will not succeed in anything without putting in the time. Maybe there are people who simply claim to "not study all that much", but are you with them 24/7 to see what they are doing. I've known people who get off on bragging that they didn't really study all that much, when in reality they stayed up half the night. Also, there will be some people who may just have more experience with certain concepts, or simply were better taught in undergrad. For instance, I started learning MSK and systems anatomy in 1st year of my undergrad, and then was lucky to work as a teaching and lab assistant for the same course, so I had 4 years of 'general' anatomy knowledge coming into grad school. So obviously I had a bit of an advantage - in terms of not having to put in as many hours as someone who'd never seen a cadaver. But I still had so much more to learn, and was still studying daily to memorize all the things I didn't know.
So what I'm saying is, put the time in and don't worry about other people. Some are just lucky to have some more experience and others may not be telling the whole truth. But noone gets As in anatomy, for instance, by sitting around watching TV night after night.
My advice to you would be:
1. Read lecture notes before lecture - everyone has said this from day 1 of undergrad and honestly I didn't listen until 4 years later, but it makes so much difference!
2. Don't feel the pressure to read every single page of every text book. Your lectures should cover the most important topics. Refer to textbook resources to clarify things you don't know. Unless your prof says that a reading is mandatory, I would leave it at the bottom of my 'to do' list. There is no need to spending hours reading things you already know.
3. Don't take notes from textbooks!!!! In 1st year, all us keeners thought it would be helpful to 'make notes'. So I bought a notepad and pretty much re-wrote my biology book. It didn't help at all, just wasted time. In the end, I never have time to review my notes...and I write too much anyway. Since then, I simply started taking notes in the texts or on my lectures or sticking little post-its into texts and highlighting.
4. Practice questions, practice questions!! Do as many practice questions from old tests, textbooks, online as you can. Then study things you don't know! Don't waste time reviewing things you know 100x over.
5. Take breaks. Don't spend every waking hour studying. Get involved in something, so that you have an activity outside of school to look forward to. For me it was intramural sports/gym. Maybe join a school club? Volunteer? Go to the gym? Anything to force yourself to leave your house a couple times a week!
6. Unless you have tests or quizzes on Saturdays, Friday is a mandatory night off! Go hang out with your friends, watch a movie, go to the bar or the gym. But you are not to touch anything school related between 6pm Friday and 10am Saturday - it's the law!