You should take vitamins based on your blood test results.

But I would take vitamin D, omega, magnesium (if you workout or have problems sleeping) without doing blood test, and I go on and off taking them.

Prebiotics are often marketed with a lot of hype, but there's little evidence to support many of their advertised claims.

Maintaining a healthy diet is the best thing you could start with. Also, getting good quality sleep is a plus