I own 4 paper airplane books and have made countless other airplanes/gliders from instructions on the internet. Nothing I've seen or made beats this very simple airplane for long distance floating/gliding.
The quick instructions: Make a standard dart with one piece of paper and halfway make another standard dart with the other piece of paper. Tape the completed dart to the bottom of the half completed one and you're done.
For detailed instructions follow the steps.
Step 1: Supplies Needed
2 sheets of photocopy paper (8.5 x 11) and transparent tape
Step 2: Start Making Two Standard Airplanes You Made in Grade School
With each piece of paper, start making the standard "dart" every kid makes in elementary school.
On the one on the right I taped it closed. (You may not be able to easily see the transparent piece of tape). Set this taped one aside.
Take the one on the left and keep making the standard "dart" airplane by folding it in half (valley fold) then folding the wings down (steps not shown here or on the next page). See next step to know where to fold the wings
Step 3: One Completed Airplane
There are many angles you can use to fold the wings. For this glider, you fold the wing down to exactly meet the bottom edge of the keel. (the part you hold when you throw it). The wing edge should meet the bottom of the keel from the very tip to the very end. This pictures shows both wings folded down.
Turn your dart over, spread the wings and tape the two halves together. (You may not be able to easily see the transparent tape).
Step 5: Tape the Dart to the Other Piece
Now take the half-completed airplane you set aside earlier. Turn your completed dart upside down and line it up as seen in the photo. Align the points exactly. The back of the dart should be centered between the outer edges of the bottom piece. Tape the dart to the bottom piece--one piece of tape for each wing. (You may not be able to easily see the transparent tape on each wing).
Step 6: Completed Glider--back View
This just shows how it will look from the back.
You are done!
Throw it and watch it float forever--due to that large wingspan.