Some of the things we do to help:
1. Declare actions ahead of time. Everyone states what they are going to do, round robin. This acts as an overview of the round to come, reduces decision-making time during the actual round, eliminates actions that cause someone to have to do something else, and gives everyone an idea of what they need to roll ahead of time.
2. Everyone rolls at the same time, where that is actually possible. Most of the time, it isn't possible, because of the way combat flows in D&D, but when it is, it is a huge time saver.
3. We get all of that out of the way FIRST. We do description SECOND, and all together. It is an interesting effect, but the "reward" at the end of each round, even though it is actually less quantity, seems to be of higher quality, and has more narrative flow to it.