I printed labels (30 per page) that said "Please join us Thursday 6 pm in the media center for our PTO meeting."
I had the teachers "stick" each of their students on Tues, Wed or Thurs. We had about 6-8 more parents than usual. We usually only have about 3 parents that aren't teachers.
We are also having signs printed that say the same things and we will put them out on the Monday before.
I think alot of people just don't know when the meetings are or forget.