Best rule, especially when you don't know your plant, is to remove no more than one-third of total growth at any one time.
As with most plants, if you chop off its head (remove top growth), you'll be encouraging a squatter, more bushy plant. If you remove side growth, you'll be encouraging a taller, skinny plant.
As long as you keep to the one-third only rule, you won't harm the plant.