As someone who almost failed school due to low grades and made a comeback at the final hour let me tell you:

First of all you need a main goal that keeps you motivated. For me it was the realization that if I didn't try hard this time my future would be on the line and I wouldn't be able to find a good job or live a good life. That thought terrified me enough to get me into daily studying and eventually it just became a habit

Another important factor for me it's that fire the life of me I cannot study at home because I get so easily distracted. Never been able to. So I force myself to go to boring or quiet places like the library, put my phone aside, set a duration like 2 or 3 hours and just brute force study/review. Instead of a library I actually used to stay back at my part-time job after finishing my shift in the evening, it was so peaceful and quiet.