Always check with the business where the board is located, ask if it is acceptable to post something. Most are not moderated, but you will run into a few that are and you can usually tell by how they are arranged (nice and neat, or messy and outdated).
Sizing your ad: I've found smaller postings (4" by 6" or 5" by 7") work best as they are less likely to be partially covered up by someone else's flyer.
Make sure your advertisement stands out! Use bright colors, bold lettering or make your ad really different. I really like to add business cards to my bulletin board posts, so I usually make a flyer that can support a holder and then add 10 to 20 cards to it.
If you use my example as a template (or use a tear-away template), make sure to include contact information on the flyer elsewhere so if they run out interested folks can still get in touch!
I love to add QR codes as many folks use their phones to save information for later while they are out and about. You can get free QR codes @ https://www.qrstuff.com.
When you receive new requests or a new customer, remember to ask them where they found you! Tracking this stat can help you better prepare future bulletin board ad campaigns!
I hope you've found these tips helpful! If you've created a unique bulletin board campaign, I'd love for you to share!