how to prevent bloating and belcning
It depends on what is causing the bloating and belching. You can read this article on excessive gas in the upper gut. http://www.healthhype.com/excessive-gas-in-the-upper-gut-stomach-intestinal-causes.html
Once you can identify the most likely cause in your case then it is a matter of avoiding the trigger factors. If you have any GI disorder, then you may need to see a doctor who can prescribe the appropriate treatment. This will help your symptoms like belching and bloating to resolve.