I've been seeing these pennant garlands around lately (like here and here) and my own little front porch was just crying out for some of the same treatment, so I riffled around in my scrap basket and in two shakes, had this to report.
Aren't they loverly? They're the simplest thing ever, and you'll need neither a pattern nor a tutorial, but just in case, here's what to do:
Draw yourself a goodly triangle, isosceles if you don't mind. Don't be getting out your protractor, I don't know what kind of an angle I used—just make it so it looks nice to you. My pennants are about 12" on the long side, with a maybe 50 degree angle at the point? If there are more proper geometry terms than these, may I remind you that I am too old to be remembering all that stuff...
Now you can make a paper pattern of your triangle if you want, but I just went ahead and cut it out of the fabric. I use a self-healing mat and rotary cutter, and a clear acrylic quilter's rule, and if you don't have these things, I do truly recommend them all; they are unbeatable for getting a super-accurate straight line (and the ruler also has angles to measure by if you are inclined to be that way.) Keep going with other fabrics, cutting all the triangles to match the first one (or, heck, you could have all different triangles if you want—that would look nifty, too.) I cut two of each triangle.
With right sides together, stitch a ¼" seam along the two long sides of the triangle, leaving the short side (the top) open. Turn it and press. Do that to all of them.
Now take a length of 1" double fold bias tape and open out one of the folds. Pin it to the top of one of the triangles, with raw edges aligned. Keep pinning the tape to the triangles until you have run out of either tape or triangles. I made my garland with the corners of the triangles touching, but you can do this your own way.
Stitch the tape to the triangles using a very scant ¼" seam. I tried to stitch just toward the raw edge side of the fold in the tape. Then, fold the tape over to the other side and stitch it down, as close to the edge as possible. That's it! Hang it where it will flutter gently in the breeze and your house will look like a festival tent. Invite some friends over, sit on the porch with a sweating glass of something fruity, and watch the world go by.