Before I do a commission for someone I fill out a sheet with all the information for the project. My commission sheet has
*I want more than one way to contact my client. If I am shipping the art it's extremely important to have the address exactly right and you can double check it online at USPS.com
Type of commission (i.e. concept painting, portrait, or design work)
Reference material - Does it need to be returned? Watch out for copyrighted material.
Materials Needed and Cost - This is always different, make sure you know what you will need and how much it is going to cost before you give a quote. I sometimes ask for a deposit in this amount so I'm not out the materials cost if the client backs out.
Size - This is an important aspect for me since I use pre-stretched canvases. I usually get an idea of size then I have to tell the client what sizes are available. This may take some research on your part. Can you get it locally? How long will it take if you have to order it? Works on paper are similar, I try to feel out the client for how much they want to spend on framing.
*I never frame my works on paper, I rather the client find a framer in their area where they can pick out the frame, matting, and glass. These options start to add up and the time for framing can vary from a week to 4 weeks.
Price - Everyone has their own pricing system, but agree ahead of time how much this will cost and do not add to that total without consulting your client, nothing would be worse then for your client to have to pay more in the end because you decided to change materials or it took you longer than you thought it would. Allow yourself some wiggle room when you give a quote. Offer a payment plan if needed and then outline when you expect to be paid with dates and your accepted payment methods (check, cash, PayPal, etc.).
Shipping - Never include shipping in the price of the piece, cost of shipping can change based on fuel costs, always arrange for them to pay the shipping about a week before delivery, then follow through and ship the art on time and packed well.
Timeline - For large pieces that will take several months to complete I set up a timeline with multiple deadlines along the way so that there is a set of expectations already outlined and the client isn't contacting me randomly.
Deposit - Decide whether you will require a deposit, I usually ask for the cost of materials at a minimum.
What they get with the commission - Certificate of Authenticity, Instructions for Care, and Free Delivery within my hometown are a few of the things I give to all my commissions.
If possible get the client to sign the agreement, especially if it's a lot of money.
Hope this helps.