This is one of those things that’s extremely simple yet effective. I have a magnetic whiteboard hung near my gaming area so imprinted up some magnetic labels with the names and AC’s of all of the player characters along with some generic labels that can represent groups of enemy combatants.
When initiative is rolled I rearrange them in order on the board so that everyone has ample warning when their turn is coming. If someone delays their action the labels can be shifted around as needed. It’s nothing fancy but it helps keep combat encounters moving along.