Deciding how much to trim is basically comes down to how you want the plant to grow. A lot of people say I trim way too much off my plants but i think the end result speaks for itself. I eventually trim off everything below the FIM and above it to about 1/3 from the soil level. The basic rule of thumb is 1/4-1/3 off the bottom but my trimming doesnt stop there. The goal is for all crowns/future main colas to receive as much light and as much food as possible so any small branches that get minimal light (like the lower 1/3 of the plant) are removed. The plant can then focus all of its energy and nutrient intake towards the main colas instead of wasting some of it on sucker branches that end up producing minimal bud. I also trim up all the crowns/branches the same way by taking off all the lower growth so again the plant is forced to focus its energy on growing that main cola bigger and taller. It also allows more light to get through the whole plant so crowns/branches that would usually be shaded now have more lighting so they can stretch out and reach up into the canopy to become a main cola. I'll add some pics to give you a better idea.
At first its very hard to cut so much off your plants and leave them looking a bit bare because it seems like your sacrificing yield. But you soon realize that is not the case when your recently thinned out plant is now bigger and bushier than you expected.
My trimming starts when I FIM and continues weekly-fortnightly all the way through veg and even the first 4 weeks of flower but not as much needs to be trimmed at that time.
These pics are of a plant and one of its branches just after trimming so you can see where the lower growth was removed on the branching to encourage more overall growth to that branch.
Then 2-3 days later
Then 7 days later and so on
That branch from he first pics
Some pics of week 1-4 of flower
Heres some more random pics of the trimming below the canopy at various stages.
most peeps have moved sites, cud do without losing another top grower
. Ive even had to give up the growing due to work commitments which dont leave me much time (or energy) to tend to any plants 
. I do check in here as often I can but unfortunately I havnt had enough time lately to read everything and reply to everyone but I do see all your posts. I am trying to reply to everyones PM's as well so I apologize for the delay. I still like to use some of the time I spend on here to quietly browse new threads and catch up on a few journals that interest me but I havnt forgotten about you all, just hard to fit you all in.
. Keep up the good work mate 
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