The biggest problem for Kingdra is being Ferrothorn bait. Make sure your team has a safe switch-in for Ferro lest you want to suffer a slow spiky death D:
I guess you can give Kingdra HP Fire to effectively lure and kill Ferro, but it's not even a guaranteed 3HKO in the rain.
Outside of Ferrothorn, it's a solid mon. I've been using a slightly gimmicky set with DD - Outrage - Hydro Pump - Draco Meteor @ Dragon Fang with decent results. Max SpA, enough Speed to be faster than Jolly Breloom, rest in Attack; Mild / Rash Nature. Lure in physical walls that tries to stop DD Kingdra, only to punish them with Hydro Pump & Draco Meteor. People think that Kingdra is forced to switch out after the special drop from Draco Meteor, only to meet with a DD-boosted Outrage >:D. You can try Surf @ LO for a more accurate Water STAB and for a bit more bite on its Outrage and Draco Meteor than DFang's 20% boost.
Other than the above set, you can't go wrong with Max SpA / Max Spe Timid LO Special Rain Dance Kingdra - Rain Dance / Hydro Pump / Ice Beam / Draco Meteor. You should have no problem being revenge-killed thanks to Swift Swim :)