As I ask for parent volunteers, I refer to this site. It has a few examples of obstacles parents may come to you with in regards to volunteering. Each obstacle gives a few options on how you can tackle the problem and involve the parent.
Teachers may worry that having a parent volunteer will require them to cut out instruction time in order to get parents going on tasks. Having a parent binder is the solution. This resource has tips and printouts for getting your binder started.
Running out of ways to use your parent volunteers? Sometimes it can be hard to find something to do when you are wrapped up in the daily grind. This list has 50 ways that you can utilize parents in and out of your classroom.