Peckish

Make sure you are thoroughly covered with insurance, for your machine, for your customers' quilts, for any slip-n-falls on your property, etc.
Obtain the requisite business and resale licenses. (Resale, because often customers want to purchase batting from you. You buy wholesale and sell retail, so more profit for you, but if there is sales tax in your state, you will need to collect and report it.) I have a longarmer friend who will only quilt and sell one brand of batting because it works so well with her machines.

This is VERY important: Have very clear and specific intake and contract forms that specify what you will do, won't do, what the customer wants, does not want, quilt design name, quilt flimsy description and measurements, pricing info, half paid up front for deposit, customer signature etc. Quilt description and measurements are very important. Same longarm friend once paid me to completely unquilt a queen sized quilt because her customer had brought in 2 blue quilts, the intake form did not differentiate clearly enough between the two, she got them mixed up and quilted an all-over panto on the appliqued flimsy that was supposed to be custom quilted.

Do not let customers take advantage of you or guilt you into discounts. It is not YOUR responsibility to make their hobby affordable. On the flip side, while you are learning, price accordingly and make it very clear the customer is receiving a temporary discount because you are learning. If there are any mistakes you will do what you can to rectify the problem, but if the quilt is to be a family heirloom, they might want to use a different quilter or hold off until you feel you are ready to quilt it.

Make them choose a pattern before leaving the quilt with you and get the pattern name and their approval in writing.

If your business will be in your home, it would be very wise to have a separate entry into your work space, and that your "studio" can be closed off from your home. A lot of people will expect that you let them use the bathroom, get a glass of water, etc, which of course is up to you, but be careful with this. You would not believe the number of people who feel they have a right to meander around your home, look around, help themselves to cookies or a glass of lemonade, sit down and watch tv with your hubby, etc. Make it as professional as you can.

Most importantly - once you start a business, you have to realize you WILL BE RUNNING A BUSINESS. I work for a CPA firm and we have a LOT of clients who loved what they did as a hobby so much that they decided to open a business, but end up not able to do any of the fun stuff because guess what, now they're running a business. You stop being a baker and start being a business owner. You stop being a gardener and start being a business owner. You stop being a micro brewer and start being a business owner. You now have to manage finances and bookeeping, supplies, taxes, licenses, customers who don't pay, customers who expect miracles, and you need to track all your costs to make sure you're actually making money.

See if you can find a mentor who can help you when you first start out, someone who you can run things by and will be able to help you see and plan for obstacles before you have to hurdle them.