Tips for History / essay based A LevelsWatch this thread
For timing, I would say that every time you get set an essay for homework or anything, try to handwrite it and try to do it in the timed conditions that you'll be given in the exam just to get all the practice in.
Specifically for history, I would suggest having really good knowledge on the specific subject before writing the essay because a lot of the time, if you have the knowledge on the page then you can get a lot of the marks.
And if you struggle with the planning part, my politics teacher always says that it sometimes helps to leave the introduction to last, so leave half a page before writing and then come back to it so you can clearly outline your argument. But a lot of people waste time on the introduction when all you really need to do is state your argument and then say what you will be discussing in the essay.
Another useful one for English : https://www.amazon.co.uk/Studying-En.../dp/0521690145