Grab a couple worlds, make repair bays, and turtle up as best you can.  If your allies are in a really secure position, they should be able to feed you to keep you alive, or at least make you a tremendously costly pain to kill.  Sometimes you will still die, but the point is to hold out long enough that your allies gain the upper hand.  Basically, you die, but 2 of your opponents die to your allies.

If, however, your allies suck....then you are probably dead.  But if they sucked, this allows you to move on to the next game where you don't have sucky allies, so it is a blessing in disguise.

I always find myself in this position. Very rarely I live long enough to retreat to my allie's side.

Depending on map size, your race, and what races surround you really only have two choices. Turtle or Spread.

If you're going to spread, get the colonizer cap first and run. If you're gouing to turtle, get the battleship and build static D. If your allies can feed you, you could have a massive fleet fast