2. The Two Bin System

In every place that you have a trash can in your home, make sure to place a Single Stream Recycling receptacle next to it. When your guests go to your "little waste centers", you'll be forcing your guests to think about the material they have just used for consumption before opting to place it in a trash or recycling collection container. If you give them the option to recycle next to the trash, more often than not, they will choose the correct container for disposal of their waste.
Also, if you are anticipating higher volumes of waste/recycling from your party, make sure to have trash and recycling collection points in more than one area of your home so that all guests will have access to a recycling option.
Note: Don't force your guests to go to your garage to recycle. The inconvenience of going outside of the house will more than likely cause your guests to throw their recycling away with the trash!
* Educational Posters
Educating your guests on the waste practices in your home will be key! If you have kids, consider making some signs that are recycling AND Fourth of July themed that can be adhered to your trash or recycling bins that remind guests to ThinkBeforeYouThrow! Simple signage goes a long way when trying to remind people to recycle.
3. Jugs & Pitchers!

It's a sure bet that the Fourth of July will be HOT! Of course it's always a smart idea to have plenty of water on hand to keep your party guests hydrated throughout the day. Although they are recyclable, plastic water bottles still create a LOT of waste at a party that will then require energy to process at a recycling plant.
A 'greener' option is to serve your guests using large water jugs or pitchers placed about your party. These can be easily refilled using filtered tap water, lemonade, or tea and served into re-usable cups.
Fill clear jugs with lemon, lime, cucumber, basil, blueberries, strawberries, or other summery things to add to your party decor for the afternoon!
4. Look for Local Firework Displays!

One of the great traditions of the Fourth of July is also an environmental faux-pas. That is, the lighting of fireworks. Many may not be aware of the amount of aluminum and particulates that are released and drop down into our soil as a result of these spectacular light shows. If you intend to light fireworks off at home, try looking for brands of fireworks that are rich in nitrogen as an alternative. These may be a bit more expensive, but create less of an environmental impact than others.
A great option, however, is to participate in a local fireworks display which gives the 'best bang for the environment's buck!' Many, many people can gather to witness the spectacle without having widespread environmental impact throughout your community.
Besides, these shows are bigger and better, anyway :)
Have a very Happy Fourth of July!