I see a lot of the same questions being asked over and over, so I'm going to attempt to address one or two of them.
WEAVING: It is rare that you will "weave" your plants into the screen. After you have some experience working a scrog, you may use that technique to hold a straggler in place, or help a weaker stem support a bigger bud. To weave means to incorporate into the screen. That is done by running a stem under and over the netting. For the most part, you do not want to do this. Should you need to move that branch later, good luck. The technique utilizes a method that is VERY easy to understand, however it does indeed take a little practice to make the most of your scrog.
The proper technique involves training the growth tips. When a top comes up through the screen, allow it to grow a couple of inches, then pull it back down under the screen and stretch it away from the plant's base to the next spot on the screen. I usually try to stretch my tops out by 2 or 3 squares per scrog session. If the top won't reach, I leave it alone until the following day, when it is a bit longer and can reach to the next spot.
By doing this, we are forcing the plant growth to go horizontal. EVERY node below the screen will receive auxin, a hormone that will cause branching. Every one of those nodes below will start branching out and then up, striving for light. What I do is top my plants before they even go into the tent. My goal is 4 strong tops. I generally leave 3-4 nodes of the plant when i top, so each one of those lower nodes will develop into a thick branch, able to support a smaller network of branches that will grow from it.
I like to work my tops out in the pattern of an "X" The 4 main tops get stretched out into the "X" pattern, and any branches off of the main branches, will be trained to fill in the middles. This is the easiest pattern to follow. I've seen people use a box pattern and a circle. The choice is yours.
When to Flower?: Deciding when to flower is a personal choice. No one can tell you that you need to begin flowering on a set calendar. However, we all strive for that 'perfect' window to flip our lights. When scrogging, we have a concern or two as to when that time comes. I've seen several misconceptions on this topic. Number one, do not wait until your screen is full before flipping the lights to the flower cycle. Why?, you ask, because, once you start flowering, the plant is going to go into stretch mode. The top few nodes are really going to stretch apart and prepare themselves of handling the weight of a cola.
The new growth that accompanies the stretch will have nowhere to go if you have already filled out the screen. As I said, I work my mains into an "X" pattern. The secondary branches that come from those branches are encouraged to stretch to the ends of the screen and fill in the empty portions on the edges. The branches that come later in the plant's life will be used to fill the middles, that are closer to the main branches.
The trick to timing the light cycle is to know your strain. In order to find the sweet spot, you have to know how much more growth the plants are capable of. Once you have filled the corners of your screen and have about 80% of the middles filled in, flip your lights. At this point, you'll continue to work the scrog and train the plants for about ten more days, until the screen is nearly full, at which point you can take a break from working the top, and get below the screen and start removing any growth that will not be receiving light. A well done scrog will not be getting any light below the canopy.
PRUNING: If you are one of the ones that refuse to remove a leave or cut off a perfectly good branch, scrogging may not be for you. In order to get a head start on branching, many growers that utilize a scrog will top their plants. They may also FIM or LST them. Controlling the growth and pace of the plant is essential when growing in a scrog. Growers will have to prune tops to encourage branching, and the amount of fan leaves that are removed is nothing short of a harvest in itself.
I have spent over an hour at a time, cleaning up under the canopy and while doing so, routinely fill 1-2 plastic Wal*mart bags with leaves. I try to tuck huge fan leaves that are shading other tops at the screen, back into the netting. If they refuse to cooperate and insist on blocking a site, I pluck the leaf. I have no aversions to taking off fan leaves. If you are scrog growing, you have to be able to remove leaves and feel good about it. You are not going to decrease your harvest. If anything, growing on a scrog increases it by four fold.
I didn't intend to write a novel, just wanted to cover a few topics that I see being discussed the most.