Rinsing your mouth after flossing and brushing helps to remove any last hidden bacteria and also helps to inhibit the buildup of bacteria until your next round of mouth cleaning. This is an important step to maintain your gums too.
Mouthwash should be both gargled and swished around the mouth vigorously for a period of around twenty seconds, or as instructed on the label.
The best balance between safety and effectiveness comes through using a salt water mouth rinse solution you prepare yourself at home. Bacteria thrives in an acidic environment but by rinsing and gargling salt water you leave your mouth in a more alkaline state that is not at all hospitable to unwanted guests.
The simplest way to make a salt water mouthrinse is to add a teaspoon of salt (preferably pure sea salt) to a cup of hot water and mix. The water is heated enough to allow the salt to fully dissolve. If you can handle the flavor, add as much salt as will dissolve in the rinse to make it as potent as possible. If you have difficulty with the salty flavor or simply prefer something a little more tasty, try adding a drop of spearmint oil and a drop of tea tree oil.
You may wish to consider using a commercially created mouthwash for a short period of time as they can be highly effective in killing bacteria quickly. However commercial mouthwashes do tend to have adverse effects so limit their use to two weeks only. Avoid use of mouthwashes containing alcohol, such as the well known brand Listerine for example. Alcohol in mouthwash has been linked to mouth cancer and over time can actually lead to a dry mouth which accelerates bacteria buildup, the opposite of what we want to achieve. This is one reason why some people report having bad breath even after using such mouthwashes for a lengthy period of time!
If you do wish to use a commercial mouthwash the most effective option is one containing the active ingredient chlorhexidine, an anti-microbial agent, for which you will need to obtain a prescription. If you use it in conjunction with a saltwater rinse you will have to use it last so as not to remove it from the mouth. Be aware it is known to taste particularly bad and after two weeks will begin to alter your sense of flavor. It is also not advised for use by pregnant or nursing mothers. This type of mouthwash is certainly effective, but it should be used for a definite limited period of time and only if you absolutely need to.