Make a timeline of everything that needs to be done. A party planning checklist can become your best friend when you're in a time crunch.
Make sure to take pictures of ALL your guests, not just your favorite few.
Send out thank you notes to those guests who came bearing gifts. A nice touch is to include a photo of that person at the party.
Ask for help! Since a picnic is such an informal occasion, it's okay to ask guests and family members to help pitch in. Be sure to have tasks/suggestions ready.
Don't
Forget to give your guests fair warning.
Forget to ask the neighbors to an outdoor party to avoid hurt feelings or annoyance with the noise level. It's a thoughtful-and smart-gesture.
Forget to bring extra chairs and portable tables for last-minute guests.