People that say they go drinking every night or whatever and still find the work easy are lying. University isn't meant to be easy.
Speak for yourself. I managed a 2:1 BSc despite missing a crap load of lectures in my final year. Research project and exams went well, and I managed my coursework fine. It helped I found my degree interesting, and I'm in a relevant job I enjoy getting an above average salary.
And I was drinking and eating kebabs 5 days out of 7 for 4 years (Scotland)

Best advice I can give if you want a decent grade: treat university like a job. Regardless of lectures, go in the morning and work all day. I wasted so many hours by going home after lectures in the early afternoon, thinking I would study there. It almost never happened. My coursemates often stayed in the faculty until the early evening getting work done and many of them got better grades as a result.
This is good advice to the OP, whatever your lifestyle you've got to put the effort in and do it, as nobody will do it for you. Understanding what you are expexted to achieve, and then knowing if you've achieved it, is important.
However if you are having difficulty in grasping concepts that are clearly explained to you, then maybe you need a rethink.