I don't trim any at all. My first experience trimming stressed the plant so bad it went male! Look, the best advice I can give you, as a new grower, just leave it alone. Seriously, just leave it alone and let it grow. Don't worry about pH, don't worry about adding CO2, don't bother trimming or pruning or LST or any of that other crap. Just focus on the basics, man. Keep it simple!