Although it's quality not quantity that's important, first drafts don't have to be perfect so it's OK to write them quicker. Quality comes with the rewrites. Up to today, I've written 4160 words of Fangtooth. Not bad (for me) in 3 days. Yesterday I realised that chapter 3 was going to be another one that needed information I didn't have to hand, so I've skipped it until later. I believe it's okay to skip chapters as long as you know that if something important is going to occur in said chapter that will reflect in another chapter, you make note of it. If you spent the time trying to find the information, you stop writing. I think it's better to keep writing. Unless vital to the story, any facts can be gleaned later.
With regard writing in general, if you're anything like me, you left school thinking you knew everything there was to know about stringing a few words together. How wrong I was. It's only in the last few years my shortcomings have been made evident. By reading books such as 'The Elements of Style' by William Strunk and E.B. White, and 'Self Editing for Fiction Writers' by Renni Browne and Dave King, I've learned a lot. I cannot recommend these books enough for anyone who wants to improve their writing. Like any other job, you only improve if you learn how to use the tools of the trade. In this case the tools are words. It's also useful to read a lot. See how other people construct a sentence. How they can make the words come alive, how they make a character or place seem real.
Other books I would recommend reading are: 'Writing Horror Fiction' by Guy N. Smith, 'Writing Horror' by Edo Van Belkom, 'The Complete Idiots Guide to Writing a Novel' by Tom Monteleone and 'On Writing' by Stephen King. If nothing else, it's good to see how other authors work.