Figured I'd toss my .02 into the pile.
I have the Foodsaver V2820
It's interesting the comments about pre-freezing. I am not quite patient enough for that approach and we don't have the extra freezer space regrardless.
My technique:
Main species for freezing: Salmon, halibut, lingcod
1. Clean and cut fish into a variety of portion sizes depending on the family stockpile.
2. Prepare cut-to-fit bags off of roll. I ALWAYS double seal. It may take a bit longer(especially since the sealing element has to cool) but I have never had a blown seal. I also put pressure on the lid simply by pushing down to insure a tight seal.
3. Put fish in bag. As others have pointed out, giving the sealing area a wipe with paper towel is key to getting a good seal. And of course again, double seal.
4. If cut into single family portions(wife, 2 year old, myself and as of last Friday a newborn baby boy!) I take an appropriate size cardboard box and stack it full. We have pretty small deep freeze and this allows them to stay tight and organized and also makes sure we are eating our way through in a chronological order. It makes a pretty good, stack-able fish cube.
Well, that's how I do it. It is certainly not the fastest way, but it keeps a good seal at a relatively low cost.