Here's a way to bind off stitches that really helps your bind off stay loose. I "unvented" it while working through Lynne Barr's mind-opening Reversible Knitting. Captions are beneath the photos.
Here I have one stitch knit.
This method helps keep the first stitch open. If you want extra insurance, you can hold it open with your thumb. I would use my left thumb to hold it open from the time I put it back onto the needle to the time I pulled the loop through both stitches.
Several stitch patterns in Reversible Knitting call for passing slipped or worked stitches over other stitches. I find this method saves time, but I don't assume that would be the case for everyone. I just fling the stitch back onto the needle when I'm going in for my next stitch. Slick, if I do say so myself.