A very general rule is to set your dropper 1-1/2 times the depth of water you plan on nymphing. Water speed will vary that distance... shorter for slower water, longer for faster.
If you're not hanging up on the bottom every so often you probably aren't deep enough.
You can tie the dropper to the hook bend or eye of your large, bushy dry fly.
Nymping and tossing junk is no time for tight loops and quick stops in your casting. Think 'casting in ovals', Belgian cast... low on the back cast and more overhead on the forward cast all the time concentrating on not shocking the rig with a crisp stop.
One more hint... generally if your indicator is moving upstream something bit!
