1.
Plan your leisure time as well as your study time. It used to help me mentally when I knew that say this Friday I can just forget about everything and play video games for 4 hours straight and not feel guilty about it.
2.
Try to move work away from your study days and try to have at least one day free from any commitments if at all possible. In my case that day was Wednesday (we had no lectures on Wednesdays for some reason) and I worked weekends on 5-10hr shifts.
3.
Regarding focusing issues, first of all understand that everyone has these problems and there is nothing wrong with you. Secondly, I remember getting into environment that promoted studying and removed distractions has helped me a lot. I used to study at the Uni library quite frequently because of that. It's quiet there, all resources are available (books or online), and you can't just sit around and watch youtube videos or play games for hours. I also remember that doing homework & assignments right after the lectures has helped a lot too since what I learnt was still fresh in my memory.
4.
Having some sort of study plan helped me too. It very much depends on your goals, etc., but just as an example I used something like this back when I was preparing for my exams - Say for this exam I have to prepare 20 topics. Preparing for a topic would take me about 2 hours each, so total 40 hours is what I need to commit to to be ready; and I have 3 months or 12 weeks left until the exam. That means I gotta commit about 3-4 hours a week starting from this week to prepare myself for the upcoming exam. Then I'd stick two 2-hour "study sessions" in my calendar (a paper calendar or google calendar, doesn't matter, whatever works for you) and committed to that schedule. With the plan in place I had nothing to worry about because I knew if I studied as I had planned I would've been ready for the exam. The plan didn't work 100%, sometime I had other commitments, the other times I was just being lazy, but a poorly executed plan is better than having no plan and even then I still felt much better prepared and more at peace with my progress.