Start from the back, round out the shape, but make sure to not cut more than 1/3 of the plant within 3 months of each trimming.
This is the good, standard advice that will do no harm.
Also, some plants have specific pruning strategies, so if you want to do the for-sure right thing, the first step is identifying your plant
Your Ultimate Gardening Guide.
Rules
Start from the back, round out the shape, but make sure to not cut more than 1/3 of the plant within 3 months of each trimming.
This is the good, standard advice that will do no harm.
Also, some plants have specific pruning strategies, so if you want to do the for-sure right thing, the first step is identifying your plant