How can I have more self-discipline? I never do homework and I'm not doing well in school because I'm lazy and have no self-discipline.

 Self-discipline is the ability to control one's feelings and overcome one's weaknesses; the ability to pursue what one thinks is right despite temptations to abandon it. You already know your weakness. Now how fast do you want to fix that. Aim for a streak of a week of homework done on time. A little bit of planning will keep you ahead of the game. Know what makes you tick. Is it the reward of completion or learning. Look at your homework from that perspective and see if you can have fun with it doing combined studies with others.