You can read a lot of negative stories about ESl "schools" in China and how they turn out to be a scam operations there.

I suggest that on the basis of that information you first analyse well what you want to do, even if you operate in a Western setting. These type of "schools" can also be found in the West.

Other things to consider:
1) location, rent of roons, how mucb it takes you to pay for all that - that's a basic business plan.
2) Define the contents of the courses you want to offer for which target audience. See what the other ciompetitors offer and try to include something they don't have if there is a market for it.
3) Also look at their fees nd business terms and conditions. Can you perhaps offer better ones?
4) Does Manchester have a larger immingratiion commiunity where ESL is needed? If so, you could produce some flyers and distribute them in coffee shoips and similar places or ciommunity centres where these people meet.
5) Then, think about your own website with your own domaim.
6) I basically believe education should be free for everybody. If your operation is a business, you cannot afford to offer anything for free but to show that you are a good guy, you could perhaps offer special reduced rates for those in need. It will have a positive marketing effect.

Jusr some ideas. Other posters may add some more.