In order to stop procrastinating:

• I can get focused.
• I am capable of working through this chapter/answering these questions
• Once I have completed this assignment, I will feel good and know I given it my best effort
• All I have to do is study for an hour, and then I can have a short break
• The sooner I start, the sooner I finish
• By putting in hard work now, I will gain better results.
• Starting is the hard part, from now on I'll be fine

In exam situations:

• I can do this!
• I have prepared as well as I can
• I have done more work this time than I usually do
• I have done well in exams in the past
• It will be over in 3 hours, I can keep my focus for 3 more hours
• I will feel good when it is over and I know I gave it my best effort