How do I fix my immune system so I don't get colds so often?

Diet, supplements & A healthy diet rich in fruits & vegies & avoiding sugar, fried foods and other immune stressors, a good multivitamin, & stress-reduction techniques are a good start. Many herbs can also enhance immune function such as ashwagandha, astragalus & medicinal mushrooms like reishi. Probiotics can also help. The road to immunity by kenneth bock md is a great book on comprehensive ways to boost immunity.