I read an interesting interview with Mike Faricy over at Robert Carraher's The Dirty Lowdown blog. In it Mike says that he starts his writing day by editing the stuff he wrote the previous day. It got me thinking about my own process and I do something similar. Revising scenes that I've just written is a good habit to get into, but I'm afraid I'm not religious about it. However, I always do it the day after I've had a good day's writing. When I get into the zone and start hammering out 3k and sometimes as much as 4k words in a day (I think my record is 5k) I can tend to accidentally skip a word here and there. So It's good to proofread, I guess. When I write fastest is when there is a lot of dialog. There's a kind of rhythm, give-and-take, aspect to dialog that you can get into, and again I can tend to skip the odd word - and some of them are decidedly odd - or even get confused as to who is speaking (although that's rarer now).
One thing I have noticed is that, as I write a scene, traits emerge in the characters which make me want to change some of the later chapters. So quite often I do. I also become aware when I'm writing that what I thought was enough material for a whole chapter, can turn out to be enough for about ten lines. That happened when I was writing "The Blood Menagerie". I got near the end and realized that two of the closing chapters just didn't have enough in them to justify the space, so I ruthlessly - though, not without a pang - chopped them out. Two chapters is a lot to lose from a book and in the finish up the novel was about 65k words long, which is short for me. However, I think it is also tighter and somehow zingier without the extra baggage.
Of course editing as you go along saves work at the end. It's also easier to see whether the plot is going in a different direction and make the appropriate changes. It's easier to make adjustments to a synopsis than it is to rewrite an entire book. One of the things that helped me get into the habit of revising stuff I had just written was when I worked as a freelance journalist for a few years and had a regular column in a Sunday newspaper. Okay, so you're writing to a deadline, but if you start producing work with glaring errors, they can just drop your column. So I went over it all meticulously before I sent it in. That habit remained and it has stood me in good stead.
Excuse me while I go over what I've just written...