Hi Joe,
You could do with some training first perhaps. While you can stick tiles on, in the real world you'll be charging customers to prep their walls ready for tiling, and fixing issues that may become apparent as you strip tiles off etc, that neither you or the customer were expecting before they booked you.
It wont wash just being a wall tiler, you'll need to be a tiler, or nothing at all. And if you're a tiler you'll be doing as many floors as walls.
From a business point of view, have a free chat with a couple of accountants. You'll need to register as self-employed with HMRC. And either you or your account sort out an annual self assessment to work out how much tax you need to pay based on your profit and loss.
And make sure you do that, it can save you loads of money. I doubt you'd pay tax for a couple of years without a whole load of work suddenly coming in.
What you don't want to do, is A) call yourself a tiler because you're not. And B) print business cards off saying you're a tiler and to call you for tiling, because you're not. It wont work.
You want to make sure you can fit and cut porcelain to various surfaces including wood. And also make sure you can overcome some of the worst floors imaginable by making it fresh and new or correcting it's imperfections.
Good luck.
Stick around the lads on here are brilliant.