This book by Steve Meltzer is a fantastic resource for learning how to photograph artwork. It appears to be out of print but it's worth tracking down a used copy or checking with your library to get a copy.
Another excellent resource is Gloria Hansen's book "Digital Essentials"
This book is packed with just about everything you need to know about taking and working with digital images of your quilts. I cannot recommend this book highly enough if you are taking your own photos of your quilts to submit to juried shows. Click here to order a copy.
You can't take a good photograph without good lighting:
Digital Photography Lighting for Dummies is an excellent resource for learning about effective lighting and lighting equipment.
I cannot stress this enough - using a smart phone or table to take a photo of your quilt to submit it for jurying to a quilt or art show is not appropriate! I love my Iphone, I carry it everywhere and I take a lot of photos with it BUT I would never use it to create a digital image to submit my work to a show, magazine or a portfolio. You don't have to spend weeks and months of your life studying photography but you should learn the basics so that when you submit a photo to a show you can be confident that it is a true representation of your work. Take the time to learn how to use your digital camera and some basic photo editing software. Start with these books I recommend above and you'll be glad you did!