The usual advice — "just start" — does not work for big assignments, because the task itself is the problem: "write a 10-page paper" is too large to start.
Shrink the first step
Do not start with "write the paper." Start with "write one sentence describing what the paper argues." That takes two minutes and gets you moving.
Work backward from the deadline
Block out research, outline, first draft, and revision as separate sessions, each with its own smaller deadline. A paper due in two weeks has room for all four without any single session feeling huge.
Protect the first session
The hardest session is the first one — everything after it is editing, which feels easier. Put it on your calendar like an appointment you cannot move.