Lets face it, turn-based combat can be slow. However long you spend taking your turn, you’re waiting three or four times as long for the next one. Here is a list of game-hastening guidelines I recommend every DM issues to their players.
Announce end of turn
When you’re finished your turn, announce “turn end” or “that’s my turn over”. This saves time and avoids confusion. In particular it lets the next player know that you won’t interrupt his turn with an “also”, such as “Also, I want to make a move action” or “Also, I want to draw a weapon as a free action”.
Take your turn immediately unless interrupted
As soon as the player directly before you in initiative announces “end turn”, begin yours. Don’t want for the Dungeon Master to call your name. If something should interrupt the normal initiative order, such as a new monster entering combat or an ability used out-of-turn, whoever introduces it should call “interrupt”. It’s it’s quicker to call “interrupt” when something happens then to wait for the DM to sanction each turn.
Decide actions on the previous player’s turn
Take note of who’s in front of you in the initiative order and decide your action on his turn. As soon as he declares his end over, announce that action. This saves other players from waiting while you think. Your turn is for doing, not thinking. It’s possible that your action will be invalid by the time your turn arrives (the guy before you might kill the monster you wanted to attack), but more often than not this will speed things along.
Roll ahead of turn
If the Dungeon Master allows, roll your dice ahead of time. This method is absolutely vital in high-level D&D third edition games, where characters might roll fifteen or more dice per turn. Be honest and don’t “mike the dice”, a cheat where an unscrupulous player rolls ahead of time and re-rolls on his own turn if it misses.
Use an egg timer
For chronically slow players, use an egg timer set to thirty or sixty seconds. Each player has that amount of time to decide their actions, or else forfeit their turn.