Sweet Jesus, there's so much you need to know before opening a shop. Where should I start? I suppose I should talk about location and advertising first. Location is EVERYTHING. If you're not going to have a good location then you might as well do it out of your home. Your location alone should bring in business just by having your shop there. Advertising is important, but your physical shop can be your #1 form of advertising if you pick a good location!
Next you need to figure out what your target market is going to be. If it's going to be college kids, then I hope your rent is cheap (or that the kids have rich parents that don't care about giving them money to fix their computers!). What's the average income in your area? What's the cost of living? These are very important things to consider. For example, if the average cost of living in your area is $30,000/year and the average income is $50,000/year, then supposedly the average person has $20,000/year for unnecessary purchases.
MAKE A BUSINESS PLAN! I can't stress this enough. You need to plan for ALL EXPENSES for running the shop. Running a storefront has so many different expenses it'll make your head spin. Entryway mat rental? I'm betting you never thought about that expense. Unless you want to be lugging around a huge a$$ entryway mat and cleaning it yourself somehow, rental is the way to go. Then you've got insurance, utilities, inventory costs, etc. Whatever you think your budget should be to open the shop...DOUBLE IT! No matter how much planning you do, sh*t happens. Have at least 6 months worth of expenses saved up before you even THINK about opening the shop.
Financing is EXPENSIVE! Only use it short-term. I wouldn't recommend financing the costs to open your shop. Read the rental agreement CAREFULLY and have it looked over by your LAWYER (you should have one before you open a shop). Make sure that you understand what YOUR responsibilities are. Some owners require rent PLUS a percentage of sales. Remember that - SALES. If they have this stipulation it might limit the amount and types of inventory you can stock. If you're making a 5% margin on computer parts and the building owner requires 5% of your gross sales, those products are a wash.
Be prepared for STRESS! However stressful you think it's going to be, DOUBLE that awaits you! The 6 months of expenses you have saved up will help with that, but you'd be surprised how fast 6 months goes by. It's not uncommon for a new shop to not make ANY profit at all for the first year or two. How will you sustain yourself during that time? If you have tons of past clients you can reach profitability sooner, but you have to give them the same level of service you gave them when you were working for home otherwise they'll potentially go to your competitors.
When you have employees, you have to be a hard-a$$. Employees will try every trick in the book not to work, take off sick days when they're not really sick, etc. It's important that you be firm but fair. You're not their friend. You owe them nothing but their paycheck (assuming they do their jobs), and they owe you their time in exchange. Never mix personal and business. It never works. I personally hate being a hard-a$$, but if you don't your employees will walk all over you. None of them understand that it's like to run a business. In many ways they have it MUCH easier. Sure they earn less, but they don't work as hard as you do, nor do they have the stress that you do. And for the first year or two, they'll be making more than you do.
There's a lot more I can add but I'm getting tired. This wasn't my best post but I might come back and add more later.