You need to investigate your costs and eligibility of joining the interflora (and other) national delivery networks. That's been absolutely essential in my experience of florists - without it, you'll really struggle to get enough business. It works both ways, you'd get to prepare and deliver the orders placed by people in other shops and you also get a share of the price of orders placed in your shop for delivery by others.
Commercial contracts (hotels etc) are absolutely essential of course but also are local contacts with undertakers, local church flower committees, etc. If you can come to some agreement with the local undertakers, you've a guaranteed regular work flow.
Customer service is obviously the biggest issue. Make sure your flowers are fresh and make sure you've always got the fullest range possible in the shop for casual buyers. Our nearest florist is absolutely hopeless - last flowers I ordered for delivery died within a few years - the bunch bought from Morrisons the same day lasted twice as long for a fraction of the price - not good! Also, same shop, I called in for a bouquet on impulse and they had none - just a few buckets of assorted oddments - said it would take a couple of hours to make up a bouquet - so off to Morrisons I went instead!
Diversity is also essential. Look into other complimentary items to sell. Obvious ones are the helium balloons, arts & crafts novelty/gift items, dried flowers, vases (home and cemetery), greetings cards, maybe even chocolate/sweets gift boxes etc.
Research your space outside the shop. Is it the council owned pavement or is it your property - you may have to partially fence it off if it's your own property. You rightly highlight the need for outside display space, but is it big enough - bedding plants etc take a lot of space - also, how about christmas trees - a pile of those outside would probably do well close to a car park - is there enough space?
