I often have clients ask me if they should include their burial wishes in their Wills. I always tell them "no." Your Will is the document that outlines how you want your property divided after your death, and hopefully it will not be the first thing people are reaching for when you pass away.
Your burial wishes should be written in a separate document and kept in a safe place. You may want to give copies to your family members or clergy, as well. You can meet with a Funeral Director to do "pre-need" planning and prepay your funeral. Some of my clients have even written out the schedule for their memorial services, down to the music they want played and the type of flowers. While these may seem like morbid topics, it makes things easier on those left behind if they don't have to be making too many decisions during their time of grief.
The What If... Workbook by Gwen Morgan has an entire section devoted to end of life wishes and is a great way to have all of your important information in one place.