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
You can request an expedited review in emergencies. I used it once and the update was available about one or two days later.
However, they say, the expedited review will only be granted in limited cases. So I wouldn't use it if not absolutely necessary.
You can request the expedited review in iTunes Connect. I think the option was on the detail page for an app which is 'Waiting for Review'. There was also a list, in which cases an expedited review can be granted.