I've read that "pinching back" or pruning basil plant (ocimum basilicum) will produce a bushier, less leggy, plant.
Where on the plant do you cut?
When do you cut? How often? Does age of plant matter?
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If you are asking about Holy Basil then I have something for you. In India, this plant is very religiously sacred and has potential medicinal uses, hence this plant is common at homes in India.
This plant is sensitive one, so it need more than average attention.
If you want to have a bushy Basil, the best time to prune is when flowers have bloomed, you need to remove the upper part of stem having only flowers. Use a sharp scissor to make a cut.
Cut flowers whenever it blooms. As far as I know, age doesn't matter.
Removal of young blommed flowers will trigger for new growth. Also remove the dead leaves and dead stems till the living part.
Never over water, this will make its leaves turn black. keep in moderate sunlight. Try watering it on same time of the day (routine).
If you see some insects\spiders around it, user Neem based pesticide (diluted with water) to get them away. or try using some organic one which is available near you.
If you're talking about Ocimum basilicum, or Sweet Basil, used as a culinary herb, its the leaves you want, so its usual to pinch off any flowers which form to stop it flowering. If you're cutting regularly for use, its advisable to cut right down some of the stems to promote new growth rather than just nipping leaves off the top couple of inches all the time.