Well for starters, the fish has to be catchable. If it leaves the bed and isn't a monster I typically just move on because these fish won't be that aggressive in my experience. Once I've found a good bed to fish try to see if there is any hard cover in the bed (stick, rock, soda can, etc.) as bringing your bait around it will often trigger the fish to bite. My go to baits will be a t-rigged craw, worm, a jig, and a drop shot. Cast just past the bed and bring your lure onto it. Keep your bait on the bed for as long as possible, while just barely shaking it. Take different angles when you bring your lure through the bed and see if anyone path produces a bigger reaction from the fish, if so repeat this path. I'll normally move on after taking 10 casts with each lure if I haven't been hit yet.