In "Wandering Island Factory" I briefly talk about tidal power, so I guess I should be more specific now.
There is no shortage of designs, so I'll just focus on the two I thought were the most viable and the least expensive to implement.
I'll call the first one the straw design.
If you look at a cup of straws and imagine a wave of water in the cup, you'll realize that the air inside each straw is forced up and down as the wave goes through, no matter how small the wave is. Much like with windmills, most wave generators SUCK at harnessing small waves and breezes. But the VAST Majority of all waves are tiny.
This straw approach solves that.
A simple one-way flap valves on the tops of the straws tie the tiny puffs of thousands of straws together into enough of a constant breeze to do something with. Remember, each time the wave recedes it draws a vacuum, each time it advances it increases the pressure.
Now, lets talk about scale, because obviously straws are too tiny to be useful on an ocean. The bundles of 'straws' should be about the size of the typical wave (1-4 feet in diameter) and the height of the straws should also match the typical waves at high and low tides. They can be made to look like massive piers or even those temporary boat bridges or other useful structures or platforms.
Downsides: 'things' will get into them and start attaching to the insides of the straws. This shouldn't impede function for a long time, but it will eventually and cleaning out the straws promises to be a nightmare. Two flap valves per straw could also cause problems with troubleshooting (though flap valves are fairly foolproof).
Big storms and high waves could flood it with water, and that could pose a problem eventually too. Placing a flexible membrane between the waves and the top of the straw to make it a 'closed system' could solve a lot of this, but starts adding expense.
Think of a thousand bobble heads turned upside down, their feet glued to a board and you have an idea where this is going.
Basically it's a 55gallon barrel with a piston attaching it like a bobblehead to a superstructure. That main piston acts as a pump every time it bobs up and down. Four other pistons, like spokes on a wheel, act like pumps as the bobble head bobs in the water with the sides of the waves. A simple plastic cover keeps the barrel from filling with water when it rains or storms. The hydraulics from the pumps obviously is where we tap the power.
These are the heavily engineered versions of the straw design and the most similar to the tidal generator used in The Wandering Island Factory. It, by the way, simply used an array of floating blocks connected to each other by a piston/pump on each corner.
I'm partial to the straw design because of its simplicity.