I've been streaming for about 6 weeks, total. I usually stream 2 days a week, and my intention is to be live for about 3 hours each time. Here's what has helped my average viewer numbers, a LOT:
If it's a good stream, I have some people there, actually chatting and hanging out, STAY LIVE! Even if I said I was going to finish at 5pm, for example, if there's several people there, I am NOT leaving. I need those numbers right now! On the other hand, if it's a slow day, me and my Mom are the only viewers, and I have a few people trickle in and then have to leave, and it seems like they're not coming back that day, I may end the stream early, so it doesn't bring my average numbers down.
Another reason for this, when there's people in the chat and we're all interacting and having fun, if someone new pops in, they'll see a fun and interesting stream, and I may gain a new follower! If a new person pops in during a more boring stream, they're less likely to want to stick around, or come back. Keep the good, fun streams going as long as you can! Then, as people taper off, as soon as that number hits 3, call it a day. (Don't SAY that, of course! 😄)
This strategy has helped me keep my average viewers up, much more than just trying to stream constantly.