1 - Certified organic foods are suppose to follow rules to not have GMO's.
2 - One particular certified organic seal you can trust, but not 100% because theres at least 0.5% GMO's, is "USDA Organic".
3 - Look for the "Non GMO project verified" label. This program is not 100% in which they allow a trace amount of GMO's at a very low percentage, but way safer than other foods most of the time that are not organic.
4 - Avoid glyphosate herbicides, pesticides and other toxic chemicals.
5 - Grow your own food. But make sure the seeds you buy are non-GMO's, non-hybrid.