When should I start pruning leaves? What technique...

Pruning/defoliation is typically done at day 1 of Flower and then day 21 of flower. If you want a great source of "How to guides" check out blackdogled.com and look at the video galleries. The internodal spacing on your plant looks fine. It will vary depending on many factors but also genetic variation from strain to strain (which can also vary from plants that are even clones!).

Just remember, every healthy green leaf you remove will reduce your plants capacity to produce energy. Less healthy green leaves = less energy = less growth. Personally, I do not remove any leaf unless it has gone yellow. Cannabis has not evolved to get rid of perfectly healthy green leaves for no apparent reason. She needs every single healthy green leaf she has, to produce the energy she needs to grow her biggest and best flowers. All new growth is relying on the older leaves to make the energy for them to grow. In my opinion, there is no reason why any defoliation should occur and I see it as counter-productive. Maximum healthy green leaves = maximum energy produced = maximum growth. Hope this helps.......... Organoman.

As its already started to flower, there's not alot you can do now. Just let her grow, feed her well, she'll probably do alot of stretching now. 🌱👍

You should of done some lst on it weeks ago would of increased the yield greatly. It has just started flowering, has a way to go. If light is too far away plant will reach more. Should be about 24 inches away in vegging and about 18 to 20 in flowering for most lights. Good luck and happy growing 🌲🌲🌲👊