I have a few friends who are successful restaurant owners. (One has been on the same site for 30 years now, several refurbs, turnover just keeps going up.)
I've tried over the years to analyse what makes some work and the majority fail. (I had five years in retail management at the start of my working life and have been part owner in a music venue).
Seems to me that as well as luck, the main criteria appears to be generating a buzz about the place with the local populace. There's the majority of the marketing done right there. TBH, the buzz is very rarely to do with amazing food (Michelin starred places excepted), although it will have to be fairly consistent. I've always preferred the exact opposite as a diner, great food, not that bothered about the decor etc. Everyone who has gone that route here in Mcr. has pretty much failed. Fine dining has died a death here, not one Michelin place in the city centre. People who will spend Â£80 on a night out drinking would baulk at the idea of spending half that on a meal...
More to do with being the place to be. There's an Italian in town (that is on the site of a previously failed resto), that is one of the busiest in the whole of the UK. Turnover above six million a year. I'm not a fan of the place, went several times when it first opened, food ok, pushy waiters etc. It's cornered the market in 'ladies that lunch' and 'power meetings'. It generates a lot of divided opinions, but as a business you can't fault it.
Another friend opened up next door to a well established restaurant that had been trading for twenty years when he moved in. Soft opening, loads of promotional activity via email, website etc. Now has one of the busiest places in town and has opened another very successful place in conjunction with two partners. The established place started to die (even though their food was better) and they had to have a rethink. They now do far more marketing etc.
A vegan place has just opened up with an ex Nomu head chef. Already fully booked every weekend, just extended their weekday evening opening times. Absolutely no competition in that sector for several miles. If somebody else copies them nearby it will be interesting to see whether the local market can support two places serving such a narrow niche. Personally I'd doubt it.
The amount of tourism will affect the mix quite a lot. London can support fine dining and diversity so well because of its worldwide number one tourist destination status. Edinburgh the same. In fact a Michelin starred chef re-located there from the outskirts of Manchester specifically to chase tourist money in his quest for a second star.
So conclusion. Study the local market and don't think you can buck the trend unless there is strong tourist revenue. All IMHO.