It is true there is no RAW discussion of the secondary effects of blindness, you get your -5 to attacks and cannot make opportunity attacks.
In my game I try and apply a little common sense to the situation:
Monsters:
If the creature is in an enviroment it knows well it can move in a straight line reasonably confidently when heading towards a feature. (e.g. it knows where it was when it was blinded and it knows where a wall is, so it can head in that general direction.)
If the creature was blinded by an attack, or has been attacked this round it knows that there are enemies in those squares and can attack them (still taking the -5 penalty of course)
If the creature is disorientated (e.g. it has been pushed, pulled or slid since becomming blinded) or doesn't know its surrounds it can move in a straight line towards a feature it remembers, but would be hesitant so it would probably move at half speed, or maybe even shift and use full defence.
Blinded creatures can of course make Perception checks to try and locate enemies.
Blinded creatures might have allies that can shout it general directions, "he's in front of you KEEP HITTING HIM", or "back up to the wall" etc.
Players:
Can do whatever they like, usually including one of the above options. I would only step in if they tried to do something that was a little too unbelievable.