I'm surprised no one has suggested the LF forum. It has a different tone than APUG, but is a source I turn to as well.
http://www.largeformatphotography.info/forum/index.php
One of the first things I read on the LF site when I was just getting started was this wonderful list of all the things you can do wrong. I haven't done them all yet.
What NOT to do in large format ?
by Q.-Tuan Luong for the Large Format Page
There are more ways to ruin a photograph than you would think. All these potentially fatal mistakes are specific to large format, in the sense that most of them are impossible, or quite rare with 35mm and MF cameras. Here are some of them, and how to avoid making the mistake. Additional suggestions welcome.
Mistakes make while taking the photograph
lens not stopped down
shutter speed not adjusted
dark slide removed before closing the lens
holder with exposed film used
holder with no film used
camera fired with no film holder inside
dark slide not removed before the exposure
dark slide put back the wrong side
dark slide not put back
rear dark slide pulled out
vignetting due to internal blocking
vignetting due to excessive movements
vignetting due to compendium shade/filters
lack of depth of field
poor focussing
camera controls unlocked
camera shaken by the wind
subject shaken by the wind
reciprocity failure miscompensated
filter factor not taken into account
bellows factor not taken into account
wrong f-stop scale (with convertibles or Nikkor telephoto lenses)
change in light/subject not taken into account
cable release / shade showing in picture
mysterious double image with long exposure
Pre and post exposure mistakes
film loaded backwards
film misloaded
dusk got on the film
forgot at home tripod/holders/essential camera part
darkslide accidentaly opened
wrong developpment (ie color instead of B&W, or +1 instead of -1) applied to the film
flipping the light on before closing film boxes
Defective equipment
light leaks in camera or bellows
light leaks in holders
ground glass mis-alignment
film plane mis-aligned in holders
erratic shutter