Finding ideal king mackerel conditions means finding clear-green water, moderate current and plenty of bait.
Just because you found them there before doesn't mean the same spot will produce again - if you already caught that big one he's gone, don't be afraid to try some place new after 15-20 minutes.
Mix up your presentations, use a combination of downriggers and topwater along with different types of baits to see whats works for the day.
One that goes along for all fishing -- check the quality of your lines, hooks, tackle and knots. Something that seems so trivial could cost you a big fish.
Normally I'm pro Circle Hooks especially under catch and release conditions but the slash and fast attack of the kings make it a really poor choice. Use J-Hooks when going after them.
Hardtails are the ultimate bait, for king mackerel 8 - 12 inches is ideal. Handle them the least amount you can to keep them fresh as possible, they are hardy but the oils in your hands can do some strange things to bait.