Nervous!

ANother problem I have is this:

I'm in BB and have Q [img]/images/graemlins/spade.gif[/img] 4 [img]/images/graemlins/heart.gif[/img]
I check

Flop comes J [img]/images/graemlins/club.gif[/img] 7 [img]/images/graemlins/spade.gif[/img] 4 [img]/images/graemlins/diamond.gif[/img]

Where do I go from here? Obviously I check, but when someone bets? Do I call for one bet having 5 outs to a decent hand? Do I fold?