You're probably going to want to start with carrots as a base to your juice. And probably best to make 85% carrot with 15% broccoli, or 85% carrot with 15% cabbage.
Spinach is good but it's not going to taste good unless you add it to a tasty base. I'm not a big fan of beets but lots of people like carrot spinach beets.
A good Celery
drink is tomato, celery, dill and lemon (it's like a v8, add a drop of hot sauce and you're good to go!)
You need to be sparing with the cabbage and broccoli - they're bitter.