A good place to try out downriggers is in the salt or a deep lake.
What ever you decide to use for a lure/bait you will want to let out at least 20 feet of line before you connect your line to the ball. If you are running two DR's at the same time let out 30' of line on one rod then say 40' on the other. That way the two lines won't be banging in to each other. Then drop your ball down to the desired depth. Your pole should have a good arch to it so when a bite happens the line should break free from the release on the ball and the pole should snap back straight setting the hook in the fishes mouth.