When should i begin pruning my plants?

i am on week 4 day 4 of flower and my buds are doing pretty well. the plants themselves have a lot of foliage which blocks the lower leaves and buds from getting light. this is my first legitimate grow so im not sure if and when i should prune. i lollipopped a few times during veg and flower but not too much. i was afraid to cut off too much and hurt the plants. i have like 3 or 4 stems coming out of my main one that are pretty strong and have a decent amount of foliage and buds. i know its too late to cut those off now but i have some droopy fan leaves towards the middle of my plants. should i remove those to allow more light to come in?

No. I view every healthy leaf as a badass little solar panel providing much needed energy to aid in bud formation etc. If you have already lollipopped you are doing well. Removing middle and upper leaves is going backwards (for the most part. Sometime EXTREMELY abundant foliage or HUGE indica leaves may be trimmed. SOMETIMES) If anything I would trim the bottom buds and branches that WILL NOT get enough light. This is all my Very humble opinion.

I used to do the same as you....Hmmmm...a leaf is drooping or has some damage...I'll just remove it. The real question that needs to be addressed is WHY ARE YOUR LEAVES DROOPING?

It is now my goal to find any and all deficiencies and their cause. Having healthy green leaves until harvest is the ultimate goal. For me anyway.

I lollipop all thru veg. in flower I tuck/bend them out of the way when they are blocking lower bud sites.

The buds don't need light, the leaves do. If you really feel the need to remove leaves from your plant, keep it to a minimum.

if the buds are being blocked then the leaves are being blocked as well. lollipop all the way up until flipping, then tucking and bending leaves out of the way as best I can.

I am in the "leave that shit alone" camp. I also don'y mind some popcorn buds on the bottom to make edibles.

I'm in the prune as flowering stage happens. Leave some leaves at the top and trim the middle, a couple/few per feeding that late into flowering. The fan leaves are going to be harvested at the end for their nutrients anyways, so do you want the focus to be on the fan leaves now, or the buds? ...and yes, the bud leaves absorb light too. You want as much light penetration as possible, and taking fan leaves away this late in the game is not going to harm anything. I know this is a religion, so no disrespect to anyone -spek