During the first draft of a novel, one thing I never do, no matter how strong the temptation, is go back and start rewriting earlier chapters. For anyone writing a novel for the first time, I cannot advise you strongly enough to avoid this snare. Do not rewrite anything until you have finished your first draft.
Once, years ago, I made this rookie error. Consequently I found act two all but insurmountable, and it took every ounce of willpower to overcome the fierce George McFly syndrome that ensued (regular readers will understand what I mean by “George McFly syndrome”). The more you polish earlier sections of an unfinished novel, the more impossible finishing it will seem. The better the prose reads at the start of an unfinished novel, the worse any new writing will feel as you push on ahead.
That is why, with every novel I write, even if get brainwaves mid- draft that massively improve the book, I ensure any earlier sections affected are rewritten afterwards. The same is true if I want to include more scenes with a character earlier, more foreshadowing of character arcs, or even if I just want to make an earlier section more atmospheric, scary, funny or simply read better. No matter how good the ideas or inspiration, simply jot down the essence of them separately then return to implement your plans after you have finished the first draft.
Trust me. Heed this advice and you will save yourself a world of pain.