Green veggie juices are an acquired taste, but I like cabbage, brocoli, celery, cucumber, lettuce, basil, cilantro, etc. Cabbage is surprisingly sweet and especially good for the stomach and digestion. Start slow -- it can cause burping.
Kale, spinach, chard and other dark leafy greens are stronger in flavor, but I put a handful into a juice blend. String beans have a medium strong flavor.
Parsley is very strong -- don't drink more than 1/4 cup per day.
Adding a whole (skin and all) organic lemon gives a nice tartness as well as terrific bioflavanoids. A knob of ginger gives it zing.
I dilute the blend to taste with water.
I add some apple, carrot or beet for sweetness, though one needs to be careful not to go overboard -- their juice is high glycemic load. Adding it at the end means you add a minimum to make the mix palatable. Half an apple or one carrot per cup. Using part of a beet is messy, so I generally use one beet when I'm making a quart of juice.
My final touch is a tbs of molecularly distilled fish or cod liver oil for omega-3 fatty acids. It doesn't taste bad if it is fresh. You can get it with citrus flavor as well. It helps metabolize the beta carotene, Vitamin K and other oil soluble nutrients in the greens. Cod liver oil also provides Vitamin D, which is good in the winter.