Looking at my writing board, I've got five projects either in development or revision. Six projects if you include this blog, and I do. Plus, I'm trying to get more into freelancing, so that's seven.
So how do I juggle through all of them? Careful time management.
I always try holding an hour or two each day for drafting new material, and I rarely draft more than one project at a time.
I try keeping my drafting time in the morning so that, no matter what else happens in the day, I've at least gotten some new material down.
Two nights a week are spent working on development, either new projects coming up in the near future or adding more ideas to my idea pool. Three nights are spent working on freelance proposals and client searching. These are just for the weekdays, by the way. I prefer keeping my Saturday and Sunday evenings free to relax unless I absolutely have to catch up on something from earlier in the week.
Saturdays are mostly spent on revisions early in the morning and in the middle of the afternoon, with a writing group session and lunch in between. And then I do submissions on the last Sunday of the month. It can be a piece of flash fiction I wrote the previous week or a short story I've spent a couple of months working on, but if it's ready to go out into the pipeline, it'll happen on that final Sunday.
That's basically how I keep my writing schedule in order. If I label a block of time simply as "writing," it doesn't work because I have no idea what I'm supposed to focus on. Now, I don't always stick to this, especially given my resurgent writers block lately, but the important thing here is simply having time set aside for writing.