The easiest way to keep your garbage disposal from stinking is to give your garbage disposal a thorough cleaning on a regular basis. Use a soapy bottle brush that you have dedicated just to cleaning the garbage disposal (cause it's gonna get icky) and vigorously swab the inside of the garbage disposal. Make sure that you also get the underside of the rubber flanges that sit in the bottom of the sink. When you are doing this, put a wash cloth over the drain so you don't spatter the gunk that you'll loosen during this process.

Once the major gunk is removed from the garbage disposal, create a solution of bleach/water solution with 1 tsp of bleach mixed into 1/2 gallon of water. Pour the bleach solution into the disposal and clean again with the bottle brush. Make sure to cover the drain with a washcloth since you don't want any of the bleach solution coming out of the drain.

Once you are done, completely rinse out your brush and your garbage disposal with very hot water. Your garbage disposal should then be stink-free for weeks to come.