The only way is to buy 100% organic foods that are specifically labeled Non-GMO.
Most of the produce in the grocery store is non GMO. Except for a few:
Hawaiian grown pineapples and papayas.
Most of the GMO foods will be in products of highly processed foods.
There are not many choices at the moment. All we can do is to encourage those who do not make GMO food products is to label them as such.
See the list of companies that have GMO ingredients.
Labeling of GMO Food Products sign the petition