The farther up your line you have your ball-bearing swivel, the less twist you will get out of spoons.  I tie a 4-5' leader to use when flutter-spooning and put the swivel at the front of the leader.  Makes landing the fish a little more tricky but with the big wobbles, spins, and flips you get out of a large spoon, a swivel too close to the spoon doesn't stand a chance of eliminating the twist.

If you aren't using a ball-bearing swivel, don't even bother.  The cheapie swivels with no ball bearings are a total waste of money.  You are lucky if they even work 20% as well as a ball-bearing swivel.

If you DO get line twist, your best strategy is to just cut off all your terminal tackle and troll for a while while just feeding out bare line until you are past all of the twist.  This allows the line to untwist naturally as it passes thru the water.  5-10 minutes of this will usually do the trick.

Check your lure action and trolling speed next to the boat when using spoons.  It's easy to go too fast and destroy the action of the spoon.  Too fast and it just spins around in a way that doesn't produce fish.  You want that spoon to dance and dart around a lot, not just spin tightly.

Mylar spoons are awesome at deeper depths.  You get a ton more flash and it mimics the shiny gold or silver color of ciscoes, alewives, smelt, etc. which are the prey fish that swim deeper down and over open water.  You can even find mylar tape and add it to spoons that have none.