What is the best way to prevent botulism in food handling?

The best ways to prevent botulism in food handling are wash the raw fruits & vegetables thoroughly before using them, hands of the food handler should be clean, immediately discard the left over of many days, the preparation area should be disinfected & cleaned on a regular basis.

1) Wash your hands BEFORE and AFTER handling raw ingredients.

2) Always cook the food, especially raw protein, at the correct temperature and for the correct duration of time.

3) Never touch cooked food with your bare hands even if you washed  your hands. Always use a clean utensil when dishing a serving to your plate.

4) Always store leftover with a cover and if you are not going to consume it within  a couple of hours, put it (with the cover) in the refrigerator.

5) When cooking or eating, ALWAYS turn away from the food if you sneeze or cough.

Unless you know what you are doing do not "can" or preserve foods that need to be Pressure canned.

Do not store garlic in oil. 

Properly store low acid foods, these are the things that if you are preserving you need to do so properly. 

Keep hot foods hot, keep cold foods cold, rapidly cool hot foods and store properly. Use or freeze within 3 to 5 days. 

wash your hands. Wash the serfaces you are using. cook to proper temperature.

To prevent foodborne botulism: Use approved heat processes for commercially and home-canned foods (i.e., pressure-can low-acid foods such as corn or green beans, meat, or poultry).

It all comes down to Temperatures and Handling. Unfortunately, there are too many people that just don't care enough to handle food properly.