Aside from hand-washing, getting flu shot, etc., what are some good ways to boost the immune system during cold/flu season & avoid getting sick?

Great question!: Many people have opinions about "how" to boost the immune system. Practically speaking, there is no correct answer to this. The immune system is very complex and I am not aware of anything in particular that will globally "boost" this. A good diet, regular exercise, and an appropriate amount of sleep are good things along with the things that you are doing.

No magic pill: Many people are looking for some "magic pill" to "boost their immune system". There is no such pill. However, there is a way to boost your immune system, live a healthy lifestyle. Proper diet, proper sleep- wake cycles, healthy environment, proper exercise are the foundation of good health and good immune health. Supplements should be used selectively to supplement a healthy diet.