Things to keep in mind...A wedding reception is really a party for your guests. While you certainly the focus of the event, you want your guests to enjoy themselves and leave saying that was one of the best events they've ever attended.
You'll want to keep weather in mind since you'll be outdoors. If you've selected a summer date, chances are you're safe without the need for heaters. You'll definitely want to provide cover for everyone so a tent is pretty much a requirement. Even if it doesn't rain, it will provide a shaded area for your guests. If you know the temperature is going to be in the 90's or hotter, you may want to consider renting some industrial sized fans to keep your guests cool.
Remember, if you're guests don't feel comfortable, that may give them reason to leave.
Lighting...The sun will go down eventually and while there will be plenty of lights on the dance floor, those that aren't dancing won't want to sit in the dark. There are many options for lighting. Many guests line the edge of the tent with white Christmas lights (which provides a nice soft ambience, but not much brightness). Most tents are white because it doesn't attract heat and looks clean. That giant white canvas inside the tent is just begging for a splash of color. That's where I can help out with up lighting. I've even done logos and monograms, which adds a nice touch. If you're interested in having this for your event, just ask me. Here's some of the recent events I've done...
Power...One of the most important things to remember is to keep your DJ on a separate circuit from heaters, air conditioner, coffee pots or anything that has a heavy power draw. I tell this to all my outdoor clients and I cannot stress this enough. Don't assume that it will be OK to have the DJ and the coffee pot on the same circuit. I had an issue recently. We knew it was an issue before the night even started because the circuit breaker kept switching off and it wasn't corrected the way I advised. The power went out during the first dance and there was nothing I could do.
Other things to consider...There are several types of dance floors you can rent. Steer clear of the plastic or rubber 1x1 squares. They aren't made for grass and don't stay together very well. You're better off getting the 3x3 wood squares that are heavier and less likely to move. Be sure to leave enough room for your DJ to setup inside the tent (about 4-5 feet from the edge of the tent). The dance floor also works best in the center of the tent as opposed to being at one end and having to project sound long distance. The image on the left is the 1x1 plastic floor, the right is the 3x3 wood floor.
Make sure you've got somewhere for all your guests to park. Many of my outdoor weddings have been in the country so parking hasn't been a big issue.
If you have questions about anything, it's best to ask someone. Whether it's your caterer about food related things or myself when it comes to lighting, sound and placement. I've been doing this for 14 years and I've done a LOT of outdoor weddings in that time. I hope this post helps you out a bit!
I'll leave you with some pictures from the grad party I did just last night. There was a zero chance of rain so we opted to setup in the most most ideal spot for sound projection and usability of the photo booth. This was a beautiful home in Brighton and most of the guests stayed close to the house even though they had a tent further out in the yard.