What are some things and techniques I can do to minimize the time it takes for my apps/updates to be approved for the App Store? Do smaller updates generally take less time, and
In my experience, everything takes exactly the same amount of time. You sit in the queue for 6 days, then they review it for an hour or so (much less for updates), and you're either in, or rejected. If you are rejected, it will take a few more days to work through whatever the issue was.
So the only way to take less time, is don't be rejected. :) Seriously, though, go read the developer agreement and the "do this and we'll reject you" document.
They aren't even looking at your app for that 6 day "cooling off" period, so I can't imagine what you could do to make it go faster. (Although I've heard that there is a mechanism for expedited updates in emergencies; but I have no first-hand experience with that).