These two movesets are arguably the best for Kingdra, each aimed at fulfilling a different style of play.
Stat-Enhanced Tank Kingdra - Leftovers, Persim Berry
Rest - HP heal, cures status, helps stall
Double Team - Makes each successive Rest more worthwhile
Surf - Some people use waterfall because of flinch, but it really isn't that great. Go Surf.
Ice Beam - Grass that resist Surf and Dragon threats, freeze
Sweeper Kingdra -
Lonely or Neutral Nature
Dragon Dance - Attack and speed up
Return - 102 at max power and uses the raised Attack stat and for other Kingdra
Surf - STAB, hits two enemies (doubles)
Blizzard - High powered, Grass resist Surf, kill Dragons, freeze, hits two enemies (doubles)
I own both these Kingdras and do very well with them, both "In-Game" and against humans.
Hope you've been inspired!