Go on google maps and check out satellite images, they are all really clear and easy to spot. Look for interesting marks in the landscape like gullies or pinnacles that stick out of the water. These are all interesting features that will probably attract fish and at the very least, well worth checking out.
If you are floating around in the open water randomly hoping a giant fish will swim by, turn around and head back for the coast line. We don’t get pelagic fish like that in the UK close in. If you are looking down on endless miles of pure sand beds then go and find some reefs. Fish need a habitat to live in, be it rocky or kelpy, unless you are targeting flat fish which is different.