Your first response may be feeling bloated if you are not accustomed to large quantities of raw vegetable matter. If your elimination is not steady - these will definitely help you out!
I like some green smoothie action. Nutritionally it's not rocket science - you can mix and match pretty liberally with the concept.
Of course spinach and kale are popular bases - do be aware that variety is king. Don't do the same thing everyday - Variety is essential to prevent a build up of micronutrients. I suggest working mostly with what's in season - when it is in season.
I like spinach with peaches, apple, and a little rhubarb for tartness.
Cauliflower with strawberries, raspberries and an orange - including a little peel.
If you like you can add little bits and bobs like flax or chia seeds, a few walnuts, a raw egg or protein powder.
For me they are a quick and easy way to add 4 servings of vegetable matter into my day and because they work well with frozen fruit and veggies which are lots cheaper than fresh in the winter. Nutritionally frozen is fine - probably superior to berries that were flown in from Chile and a week old when they reach the store in the winter.