When a flounder picks up your line, you will feel the line being pulled slowly out, give the flounder line so it doesn't feel the weight of the sinker. This is the hard part, don't set the hook instantly, give the fish time to get your bait into its mouth real good. A count of twenty to thirty is usually long enough. Then take up the slack in the line and set the hook. You have a better chance of getting him in now. This is esp. effective on light tackle.