Some general sorts of things (not necessarily 4e specific).
Make sure initiative order is somewhere in the open so that everyone knows how soon they are coming up. This way, everyone can have a vague idea of their actions when their turn does come up
Is there a lot of player conversation? (should i do this? Will you flank that guy if i move here?) etc. too much is too much, if it seems to take a while, the DM should toss out "so what do you do?" to nudge the issue.
You could consider the initiative varient that was in one of the 3.x books and also in the 4e dmg. Initiative is rolled... then whomever is the highest goes first and then just continue clockwise (or counter clockwise, whatever) arund the table with the NPCs and monsters going when the DM comes up in that rotation. This way it becomes very clear every time when someone's turn is coming up.
You could also have a 1 minute timer to decide (not resolve, but decide) actions.
but other questions in general ...
whose turn seems to take the longest? Is it a certain player? a certain set of players? the DM running monsters?
Maybe the types of encounter builds the party is up against isn't well suited for the party (for instance, do you use a lot of minions but are a group mainly of defenders and strikers? -- minions are best for groups with at least a controller while solos are better for strikers, etc)
maybe you have too many players? It's hard to keep everyone engaged in combat if it's taking 10 minutes between each combat round. Fewer people does make the combat round go by faster.
Also, combat shouldn't be a chore, and if it isn't a chore then it shouldn't matter thaht it's taking a while, it should be somewhat exciting for most/all (or else don't bother doing it at all), so is the combat not engaging everyone's attention? Maybe they should be more descriptive and less mechanical.. (again, i don't know what is currently happening or the play styles so i'm just making random generic suggestions).