If you want to start simple I recommend you start with apple and carrot vegetable juicing.
You can include lemon and ginger too if you like although I find ginger is a little too strong for this delicate dish.
One additional extra I do love is celery. Apple, carrot, celery and a little juice of half a lemon.
Because I usually end up making one litre of juice I need the following
1 bag of carrots
1 bag of celery
2 green apples
juice of half a lemon
If you are just making yourself the one glass of apple and carrot juice then stick to
4 sticks of celery
1 green apple
tablespoon of juice from a lemon (or lime)
The key (as it always is with juicing) is to experiment with the different ingredients so you can find out if you prefer more or less of one of them.