I’m no expert since I haven’t really experimented much myself, but my post-exercise smoothie has the following ingredients and you can adjust the amounts of each as you like:

• Beets, of course
• Banana
• Lemon or lime
• Broccoli
• Berries (I usually use blueberries, strawberries, or raspberries, blackberries when they’re not too expensive)
• water to make it blendable and lowering the viscosity

I usually use frozen broccoli and berries for practical reasons (keeps fresh, easier to use the amount you want, cold drinks are nice), but you can use fresh if you prefer