I'm currently in my first grow, so I'm still learning as well, but I'll give any advice I can! I did a hefty pruning right at the switch. I read an article on high times that talked about increasing yeild up to 30% by pruning all the undergrowth 3-4 weeks into flowing. It said it was mainly or indica plants, some sativas. It's also risky if you over-prune that late in the game. Since I have a sativa dominant hybrid and this is my first grow, I was too nervous to try this. However, now being about two weeks from harvest, I wish I had. At least a light pruning to focus more energy on top. So I'd say give it a good clearing when you switch the light, maybe even a couple days before the switch so it can veg out a little of the stress. Then after 3-4 weeks into the switch id do some minor pruning, anything below the canopy that doesn't look like it will amount to much. Hope that helps man!