Well first figure out what caused the flat...was is a snake bite/pinch flat? if so the tire was under inflated for your weight or you hit something, pothole, curb, etc., hard causing the pinch flat or a combination of your weight and hitting something.
Second, was it a puncture? If so keep an eye out on the road in front of you and try not to ride through debris fields of sand, dirt, etc. as they often hide sharp and pointy bits of glass, metal, etc. that causes flats.
Learn how to change a tube...I'd suggest tubeless but at your weight you are likely to blow a tire.
Buy and use a tire pump...check your tires before a ride to make sure they are at the proper pressure especially at your weight.
It is part of being a rider...flats happen but you can greatly reduce them by following the above.