Don't take the measurements too seriously. Try a bit of each ingredient and change to taste. Try only a bit of leafy greens in at first to see if you like the taste. Bananas overpower veggies well.
If you don't keep fresh fruit around try canned fruits such as pineapple.
If it's too thick for you, add some water an re-blend. Try to avoid frozen berries and ice as cold beverages are harder to digest.