,Almost all vegetables taste disgusting juiced, so always juice some carrot or apple (preferably both - 'crapple') to blend with them to make them palatable.
Pineapple is another fruit you can add, but don't mix any other fruit juice with vegetable juice, it doesn't work. Tomatoes can be used to make veg juice palatable too, I just don't like tomato juice.
Beetroot juice for example tastes muddy, earthy and bitter on its own. Mix it with apple and carrot juice, chuck in a little celery juice - delicious. All the goodness of the beetroot juice and none of the bad taste.
For an example of how delicious a very simple juice can be, juice apples, carrots, celery and cucumber.
Just experiment with different veg; you can juice almost any vegetable. I have juiced spinach and Brussels sprouts as well as the more conventional juicing vegetables. Just don't forget to add the 'crapple'.