Few things I did think that might help you, as said above I would run tanks seperatly or in different sections of the shop, it will work out costing more but think of the hassle when you have new fish arriving, you would only need a few fish to be ill and it could spread to every or more tanks. Location, is it easy to park outside, bays or free parking, people cant be bothered to pay or park where they have to walk to far so easy access will help trade. Think of the shops that are near you,it helps if you have something like a news agents post office where theres constant and new customers nearby to attract especially at the beginning. On a bus route? I think alot of people find theres a new shop when they pass it not so much specifically looking for it on the net or what ever. Your best form of advertisement is your shop, 1st impressions is everything and how you attract people in, once there in its down to you to keep them there so your knowledge and friendlieness is going to be everything, but remeber you cant please everyone, I think is was a very good idea to get some experience by working in a lfs for a while, you will gain so much info from who you work with hopefully loads of right and wrong things to do then this will help you once you have your own shop. I dont want to sound horrible but because your young certain people wont like being told to do by a younger person, I am a driving instructor and have been for 2 year so since I was 24 and am very good at what I do but sometimes when I get someone who is older than there like you cant be a driving instructor or as good as someone thats been doing it for years and dont like being told how to drive by someone younger so is important your knowledge is good to shut them up, lol. I know you have to get some sort of licence to sell or keep aminals as a pet shop as my lfs was telling me recently and had to go to some vet who had to approve him otherwise they wont give you the licence. Because he didnt have any degrees in fish keeping it seemed they were reluctant to give him licence but he got it through how many years experience he had and giving right answers to questions, something for you to look into. Sorry for long message, hope you find some of this interesting if I have not already repeated what someone else has already said.