[MJL]

Another way to think is how many are in the hand and what could they be drawing to.
You are in the BB with Q [img]/images/graemlins/spade.gif[/img]3 [img]/images/graemlins/diamond.gif[/img] with the small blind and 3 limpers. The pot has $25 in it. Your flop is:
Q [img]/images/graemlins/club.gif[/img]9 [img]/images/graemlins/heart.gif[/img]3 [img]/images/graemlins/club.gif[/img] and the small blind checks.
You have Queens up but it's very vunerable to the flush, straight and even to a stronger Q if your second pair is counterfieted. Your bet should be enough to not give the pot odds to all the possible callers. If you bet $5 almost all have the odds to call. If you bet $10 and the next player has a pair and calls the pot is now $35 and the third to act only has to call $10. This is a 3.5/1 call, not ideal for a OESD or flush draw but you will frequently get the draws to call. If the third to act calls the pot is now $45 and the fourth to act and sm blind have pot odds of 4.5/1.If you bet $20 you will usually only get called by a big pair (which you beat), a person who has no care for odds, or someone who feels the implied odds of them making their hand will be strong enough (thus make it a wrong decision by not calling their bet if they hit their flush etc.)Thus the second to act calls making the pot $45 and the next to act must call $20. You controlled the pot odds to be 2.25/1.