My motto is "the faster you get it done, the more free you are" - works for me!!
So, I set myself 1 hr to write an essay (first time drafting) and if I'm really struggling, I do one body paragraph each day (so, 3 days) and then refine it later!
For Biology and Chemistry, I just get it done- you have no other option due to the content
Ancient History - HAVETO get it done, otherwise you will be lagging way behind!!
So, its simple, sit yourself down and tell yourself, "the faster I get it done, the more free I am to do revise for other subjects"
Productivity!! Dig it! (lol)