Imagine this situation, which has happened enough times now that I'm looking for a solution:
The characters are walking down a corridor in their marching order. The corridor is only 5ft wide. Their marching order has the melee characters at the front and the ranged characters at the back. They reach a door to a room and open it. Inside, some skeletons are waiting to attack! Everyone rolls for initiative, and the party does very badly; all the skeletons act first. Skeletons are of course pretty mindless, so they shamble forward and crowd around the door. Now the whole party, all six of them, is stuck in the corridor.
The problems with this are pretty clear. The ranged characters at the back can't see past five other characters to fire at the skeletons. Only the first melee character can attack as the others are stuck behind.
Now this isn't a huge problem with skeletons as they go down so easily, but imagine the same thing with much tougher creatures - it can last a while.
This situation is not much fun. How can I, as the GM, avoid it without having the creatures ignore the party if they win initiative? Alternatively, how can the party deal with the problem quickly, and get everyone into the action?