The two most common and effective ways to roll a sea kayak are the C-to-C method and the sweep method. Both techniques can be a little tricky to learn but are invaluable skills to have in your kayaking tool kit.
The C-to-C roll method—generally considered an easier option for beginners—is comprised of three main steps. It consists of the setup position (the kayaker leans forward, with the paddle parallel to the kayak and off to one side), the middle step (once capsized in a setup position, the paddle is moved perpendicular to the kayak, and pressure is applied to the furthest paddle blade), and the final lift (the kayaker pulls down on the blade and initiates a simultaneous hip flick to roll the kayak up).
The sweep method is a coming together of similar movements in one fluid motion, using paddle blade angle to generate lift. Get a step-by-step written breakdown of the sweep roll here.
Video courtesy of Online Sea Kayaking