To be a part of Google's shopping feeds, your product images must be at least 800px x 800px. The maximum file size is 10MB. Most smart phones comply with these size requirements.
Files must be JPG or PNG format.
Think of your images as being part of an online catalog. Nice looking photos will catch the shopper's eye, and cause them to stop at your store. Avoid a busy background and do not feature other items not for sale.
Take a peek at theDRIVE blog for other great photography tips: