Wasps are not necessarily a bad thing. Some of them eat other pesky insects, like mosquitoes and flies. As such, they are a necessary part of the ecology. Moreover, the so-called "solitary wasps" won't bother you if you don't bother them. It is the fierce territorial instinct of "social wasps" like the bald-faced hornet and the yellowjacket that can make them dangerous. One wasp sting is just a painful irritation, unless you happen to have an allergic reaction to the poison they inject. Multiple stings can be fatal.
With that in mind, it might be best in some circumstances to call in a professional to rid yourself of communal wasps. But if you can't afford that, or feel confident as a wasp fighter, there are some reasonably safe ways to get rid of stinging insects.
The first step might be to remove the things in your environment that attract wasps. For example, always keep your garbage cans covered in warm weather. Remove rotting fruit under fruit trees.
Next, find the nest. Often, you can watch the insects returning to their home just before nightfall. Bald hornets and most other social wasps generally nest in higher places, while yellowjackets often choose nests in the ground. If your lawn has gotten long, make sure there is no possibility of mowing over a yellow jacket nest when you get around to cutting it -- the results are immediate and unpleasant.
The best time to attack a nest with bug spray - go to the hardware store and choose one specifically for wasps- is at night, when all the wasps are home. Because they're all home, however, you don't want to stand in close proximity to the nest before you open fire.
It is definitely not recommended to knock down an aerial nest before the wasps have been subdued. They will be faster to the attack than you are to the retreat. And unlike bees, wasps can sting repeatedly.
If you don't feel comfortable making a frontal attack on a nest, there are commercial wasp traps available. It's easy enough to make one out of an old soda bottle, however -- cut off the top third and re-insert it with the nozzle down. Then put soda, beer or concentrated fruit juice in the bottom, deep enough to drown multiple insects. The wasps will readily descend through the nozzle, but then become confused and unable to fly out. Eventually, they will tire and drown.
Even a simple beer can, a third full, can be a wasp trap if hung outside. The problem with traps is that they eliminate wasps a few at a time. To truly eliminate the problem quickly, it's best to eliminate the nest.