Do i have to wait 30 minutes after a meal before brushing teeth?

No, that: recommendation comes from the theory of waiting until the saliva flow neutralizes and acidic effects from eating (about 30 minutes) and then brushing. This will reduce the possibility of brushing away slightly soften surface enamel (from effects of acids in the meal) and thus allow the natural remineralization functions of saliva. I am not aware of any viable studies on this theory...

Not at all: You can brush right away if you feel like it, especially if you have spaces between your gums or braces. Using a tooth pick or a floss first and rinsing your mouth to remove any debris or acid from sodas or juice before brushing. Good job.

When to brush: The most important point is to properly brush and floss after eating. Use a soft tooth brush and make circular movements. There is some evidence that suggests if you are eating or drinking very acidic foods or liquids it would be better to wait about 30 minutes until the saliva washes away the acid to prevent some possible loss of tooth structure.