Going out of your way to memorize a piece you're still working on is typically considered a bad idea.
By whom?
One page at a time. Luckily for me, my ability to sight read is incredible, haha. I can sight read all of the slow movements from Mozart's sonatas!Anyway! One page at a time for me. If I can play the page without making more than two mistakes, I continue to the next page until I can do the same. As soon as I go through all of the pages, I go back to page one and work my way through again, to refine all the details. And voilą!
I love looking through the whole thing, to actually experience what will be difficult and what won't be in the piece. I'll usually listen to the piece once to get an idea, then just try to play through some of the different parts. Then I section off the clear different parts, and usually just work my way through from the beginning.