I made hundreds of paper airplanes as a kid.
This design scheme was consistently among the best (not on the website above directly): http://www.10paperairplanes.com/how-to-make-paper-airplanes/...
You could also just do what I did and just fold only the top over itself, and use a bit of the back wing for the winglets, folded out. Tiny, tiny grip, enough to hold, deeper in the back than the front for stability, tiny y in the wings and winglets going out slightly. The wings need to make a y when you drop it in the air (you can simulate this while holding this so you don't mess up your shot at a perfect first flight!). Make sure to fold the front extraordinarily tightly. Otherwise it starts to tank.
Then it's a matter of how hard you launch it. As a child, I was getting shockingly long flight times, and on those special days where there was a breeze...oh boy. What a world.
Super stable, super easy to make, super easy to teach, the hardest part is the arm, the patience to keep trying, the luck that it doesn't catch in a tree, and the patience to adjust the winglets for a nice little spiral.
A lovely part of my engineering days as a child, definitely helped get the creative juices going for this field! I had a white trash bag at one point with all of these novel little designs I came up with just for funsies. :)))) :D :)))) <3