Your first priority when isolated in the open sea is to stay afloat. This means that you need to find any floating items that will support you within swimming distance. Your preference would be a life boat or raft, but any item will be better than exerting the energy required to paddle and keep yourself afloat.
If there are no floating items to hold onto and you are stranded in the ocean completely on your own, then use the following techniques to keep yourself from exerting energy from having to paddle.
Calm Water Back Floating:
Step 1: If the water is calm, then lie on your back.
Step 2: Allow your body to float, but keep your head above the water line.
Step 3: Continue to lie like this until you are rescued or come within swimming distance of land.
Rough Water Front Floating:
Step 1: If the water is rough, then lie face down in the water allowing your body to float.
Step 2: Continue to float this way until you need air.
Step 3: Lift your head from the water only to take a breath, then bring it back down again, exhaling underwater.
The rest of the steps in this guide assume that you are on a raft or other similar floatable structure that allows you to stay out of the water and move about with relative ease.