Turn the free end of the bag downward into the channel, keep the bag relatively short (a long bag is like a long beer straw, and is harder to suck the air out. Also, get the bag to lay as flat as possible, with the minimum of wrinkles. When the food saver goes from vacuum to fuse, it may let a small amount of air back in, this it typical.
I use my food saver to seal the raw meat in to marinade for a day. It is also used to extend the life of left-over portions of meat. It soon will be used to help make Sous Vide bags as well. I just have to purchase one of those fancy immersion heaters (about $170).
It can be useful to pasteurize portions. For example, you make a pulled pork, shred, put a pound of it in food saver bags, throw the bags in a 170 degree water bath for 1 hour (after sealed with the pound of meat in them). This kills any bacteria which entered the meat during shredding, and increases the shelf life (fridge life) of the meat for longer term storage.
The food saver simply increases your options for storage and food prep.