Ask for a job description of your volunteer work it provides a set of standards or expectations when you do volunteer. You don't want to set aside time to work at an agency only to arrive and find there's nothing to do. Ask about training and supervision . Its a means of personal growth . Don't be reluctant to request an evaluation of the work that you perform or a letter of recommendation.
Enthusiasm is key.
If you are not excited about the program, the less likely you will give up time in your day to go there. You get out of your volunteer work what you put into it. Please read it.