Planned right, a garden party can be an absolute hit with your guests, but there are some things you should think about before sending out invites.
Considering neighbours 'out of sight, out of mind'
Invite the Smiths one door down. Even if they don't show up, it's friendly gesture, and might keep trouble at bay. Inviting your neighbours is the nice way of warning them of noise without actually warning them. Leave them your phone number, too. It's courteous to offer a direct way of getting in touch with you if they're bothered by any noise.
Hosting a game of musical chairs
Don't assume that people are fine with standing. If your party is longer than two hours, you should have seating for at least 80% of the guests. Move
indoor seating outside when you can, and borrow folding chairs from friends.
Leaving extension cords where guests might trip
Place cords around high-traffic areas, or get metal-shaped U's at a hardware shop to clamp down cords into the grass. Don't use any extension cords outside that aren't certified and marked suitable for use with outdoor appliances.
Running out of food or drinks
For a typical party, plan for: Eight to 10 hors d'oeuvres per person, one-and-a-half burgers, or 1/2 lb of bone-in meat (like chicken wings) per person, two side dishes per person, one-and-a-half drinks per person, per hour.
Serving food guests must sit down to eat
Make sure food is fork-only. You don't want guests to struggle with more than one utensil when they're standing and mingling. So for example, if you're serving pasta salad, do tortellini, not linguini.
Going overboard on the booze
Leaving out food for too long
You shouldn't leave perishable food outside of the fridge for more than two hours, and cut that to one hour if it's very warm. Bring food out in smaller batches and replenish when necessary instead of serving everything you made all at once.
Forgetting a game plan for the rubbish
Make sure you have at least one large bin bag for every 10 people. Line bins with more than one bag so you can remove and replace full bags in one step.