In short to prevent diabetes do the following:-
1. Diet mainly from unprocessed foods, that avoids sugars and keeps grains, sweet fruits, starchy vegetables in moderation.
2. Maintain normal body weight.
3. Regular exercise; weight training and aerobic.
4. Annual checkup to monitor health. May be wise to check fasting insulin as well as glucose, and get hba1c done to be sure that average blood sugars are normal. This way you can already monitor and catch early if your blood sugar levels become less than ideal..