If you just want to look at some cool airplanes, see the last step(But building them is easy so I'd suggest that)
*** Thanks too: http://www.centennialofflight.gov/toothpick/build.htm and http://www.flyingflea.org/Toothpick/ToothpickHM8HM14.pdf for lots of inspiration in basic design and structure, but NONE of my models are directly copied from either source ***
Step 1: Begining Construction
Step 2: Wings!
Step 3: Tail Fins
Step 4: Balancing and Tuning
Firstly, to gain more side-to-side stability, bend the wings up slightly, either in the middle(Known as "Dihedral") or at the tips, this makes it so not all the lift is aimed straight down, and makes it so the plane is less likely to flip to one side(not necessary, but helps a great deal if you're having problems with this).
Secondly, you want your plane to be generally aimed up, so it doesn't dive to the ground. This can be achieved by aiming the front of the elevator down, or the wings up, I'd say about 7 degrees off from each other is good(Note the off-set of angles in the pic below).
Third thing is balance, the weight of your plane must be close to directly under the wing(as low as possible also helps for stable flight), because the wing is holding most the weight while flying. Add weight to the nose until you can balance the wings(Near the back for slower flight, like pic) on your fingers like the picture(Don't stop as soon as it's "good enough", you can always remove weight).
If you follow these steps, just about ANY airplane will work, so experiment around and have fun.
Now you have a completed airplane! Aren't you proud? Why not add some detail and originality? See next step for ideas, or skip to step 6 for flight patterns and my own models.
Step 5: Advanced Model Tricks
Still here? Greeaaat! These... Things, are good for accurate replicas, or for just nice looking planes, so if you have a specific plane you want to make, these will probably help. These things include landing gear, cambered(airfoiled) wings, bi-plane struts, plane holders, etc.
Landing gear is fairly simple and not to crucial unless you want a picture-perfect landing. They can be achieved by a simple inverted V glued to the bottom, I would suggest near the front to aid with balance, or a more square shape with a V inside it(like far left, first pic). You could also just add 2 skids to the bottom of your wings, like picture 3.
Cambered wings are said to make a glider go slower and longer, to me they also seem to help with stability and a bit of wing stiffness. To make them, simply take your wings before attaching and press about 1-2mm of the front edge under a ruler or straight edge, and bend the rest of the wing up, like picture 2(In the picture, the wing is upside-down(And crooked..)), this should make the front edge of your wing bent down, I would suggest no more then maybe 35 degrees. When attaching these wings, it may be necessary to aim them slightly higher. If they don't seem to do any good, try adjusting the camber more/less and/or aiming the wing slightly higher.
Bi(or Tri, Quad, Penta, Hexa, Septa, Octa, etc. etc....) plane struts are how you attach wings on top of each other. The most basic are 2 struts on the outside edge, but I suggest a slightly harder(and much stronger) idea I came up with. Take a strip of paper maybe 1-2mm wide, and cut into a little less than an inch length. Fold it down the middle, so they make Vs, then take both ends of the Vs and bend them out so they are level to each other. Make 2 of these. Now, mount them on your bottom wing by flipping one upside-down and gluing the bent ends to the wing, mount the other right in front/behind so the tip of the V is glued down(This may take some holding while it dries). If you're confused at this point, see picture 3. This should result in a nice 3-point platform to mount your top wings on, and it's structurally fairly strong. Most wings I've done at this point with these struts is 3, and more may be difficult due to weight issues.
Plane Holders, are really easy to make, just get a piece of squishy foam(Not stiff, the more fluffy bendy stuff), cut into something about .5"x.5"x1", then put a slice going halfway down the middle, the long way(See pic 4). You can then just put your airplanes in this crack, after gluing the whole thing to a piece of cardboard or the inside of a box(I have 23 mounted in a box for safe travel :-P).
I'd love to hear more original ideas, and if I think they're largely useful I'll post them here with credit to the submitter, but I reserve all the right to choose which I post and no offense if I don't post yours.
Step 6: Flying a Plane and Unusual Designs
Just to show that different designs work, here's some unusual ones I've made:
Quad plane, based on this:http://flickr.com/photos/jerub-baal/132671055/, flies very well.
Dual-frame Bi-plane, this was actually going to fly the other way, but I turned it around last minute :-P
Basic Mono-plane, This one was mostly a test for advanced framing and landing gear, tends to turn but flies fairly well.
Helicopter, This one is fairly old, simple rubber-powered, tends to spin out of control instantly but CAN gain some height before dying!
Basic Bi-plane, This one, with it's relatively short wings and large tail, is quite fast and smooth in the air.
Auto Gyro, Doesn't work so well :-P It was worth a try, and it coasts to the ground with almost realistic speed... But not a beginner design to be sure.
Langely Aerodrome Historic Replica, This one is heavily based of the Langely Aerodrome, originally a competitor to the Wright brothers. It flies surprisingly well, sometimes rocking from side to side but generally great.
Fokker Dr.1 Triplane, Another "historic" replica, I had to try to make one :-P It flies fairly well, main problem is it's high weight from all those wings and struts.
Twin-Tail experimental, Pretty basic, flights are ok but not the best.
Flying Wing, a surprisingly simple design, works out well due to low air friction and no added weight. However, these wings are hard to balance and very hard to tune, and you can't just chuck 'em however like the others.
Elevated-Wing Tandem, since my Langley Aerodrome model worked so well, I decided to make another tandem wing design, this time cutting the tail. It works quite smoothly, and I believe the dihedral of the wings is crucial for stable flight.
"Butterfly" Almost Flying Wing, a very simple design simply made up by my silly brother... It works pretty well, but is difficult to launch due to lack of grip points and the wings sometimes "cut", causing a fast dive.
Rear-Wing, these have always seemed the easiest to build, but I could never quite get one to work very stable. This one seems to work well due to a low center of gravity from the rudder, and from the heavy up-thrust caused by the front elevator. It has some slight stability problems, and flies fairly fast but all-in-all the lack of balance weight I think gives it an advantage in theoretical distance potential.
Basic Bi-Plane, This is a very basic plane, doesn't use the cross-struts. It flies fairly slowly and somewhat stable, probably one of my best fliers.
Random Weird Thing, I was trying for an original design :-P Ended up with the rudder in the back and elevator in the front.. It's a kinda wobley flier, but still fairly smooth.
Avro Triplane Replica, This was my replica of the Avro Triplane, built 1909-10. It's not very to-scale, but notice the British flags :-P It flies smoothly, though somewhat heavily.
Bi-Plane Canard, This was made at my grandma's house just out of boredom.. I didn't have much to counter-weight with so I made it a canard. It has a sharp turn problem, but I believe it could be fixed with slight adjustment.
More to come!
This concludes my tutorial on toothpick gliders and basic aerodynamics, I hope you find it useful and fun! Anything you're wondering just leave me a comment, and I'll try my best to answer!