You would need to start by raising a large amount of capital. Tens of millions, if not hundreds.

Now, you have two choices. "Easiest" is buying an existing, up and running cable company. There are quite a few: http://en.wikipedia.org/wiki/List_of_cable_television_compan..., and if you've got a hundred million or two in cash, I'd bet you can find a seller.

Much, much harder is finding at least one municipality willing to give you franchise rights. That's going to take a lot of time and a lot of lawyers. Franchise rights aren't cheap, and generally require an "OK" from a city council. Once you've got that, you'll can start running cables. Even more time, and plenty of that capital. Figure on a couple of years to get to the point of actually being able sign up your first customer.