Offer great service. If you want to have your own computer shop, you have to be able to provide good customer service. If you can't talk to people and break down what's wrong with their machine in layman's terms, you aren't going to keep customers. You also have to be able to decipher what problem your customer is describing, since they might not know the exact technical term for what's going on. Also, give the customer options. Make sure your customer knows that they're spending their money responsibly. For instance, if a customer has a $600 fix on a $300 machine, let them know that you don't necessarily recommend that. That way, your customers will know they can trust you, and they'll be more likely to come back as repeat customers.