Don't edit as you write
Now, this bit of advice may sound strange at first, but I really think it helps maximize your productivity.
I believe there should be a clear distinction between the process of writing and the process of editing. Editing should be a stage after the completion of your first draft and, as such, very separate to writing.
It's natural to want to check your work as you go. A touch-up here and there, especially when it comes to consistency, is absolutely fine. Sometimes reading through a page before you start can help you get back into the frame of mind from the last writing session. What I'm talking about is spending precious writing time doing mass edits and rewrites that should come later.
The reason I suggest this is that the two processes require different mindsets. The writing process is all about invoking a flow of creativity. Editing is all about being critical, sharp-eyed and analytical. Switching between the two frames of mind can be difficult when you're first starting out, and trying to do so can slow you down when you sit down to write. Separating the two process lets you focus on each area individually, giving them your full attention.
As soon as you reach the end of your manuscript —your first draft— that's when it's time to switch mindsets and become analytical. By then, you’ll have a full and rounded view of your plot, from end to end. From there, all you have to do is read through and polish the manuscript to your heart’s content.