You will need:
1. First I lay the triangle pattern on a piece of fabric that is folded over with wrong sides touching each other. That means you are going to sew on the right side of the fabric. Then, I pin the pattern on and make sure there is at least 1/2 inch all the way around the edge of the triangle for cutting after I sew.
2. Sew all the way around the triangle following the edge of the pattern as your sewing guide.
3. Unpin and use pinking shears (or your new wavy shears) to cut all the way around the triangle 1/2 inch away from the seam. Okay, one down and a million more to go!
4. Once you have sewn all the triangles that you need for the banner, it's time to print out your font for the letters. I choose an easy font because you are going to need to cut it out of felt and the less intricate snips, the better. I go with the georgia font usually. Print out the word "happy birthday" or "celebrate" or whatever you are going with in a size that is at least 3 inches tall. I print out "hapy birthd" since the extra p, a, and y aren't necessary.
5. Take your felt and a piece of Wonder Under (found at any fabric store by the yard - it has a paper backing on one side and a bumpy texture on the other) and iron the Wonder Under texture side down to the piece of felt. The directions come with the Wonder Under.
6. Before I tell you to do this part, let me say that someone must know an easier way to do this, but it's the way I prefer. I know that you can buy the felt letters pre cut in a bag with sticky backs and that can be used, but the letters are a bit small for me. So, this is the way I prefer, but it is a bit time consuming - Take the letter you have printed and lay them on the top of the felt as a pattern. I pin them on and cut them out. The felt is pretty forgiving, so cut it out and remove the paper font and see what it looks like. It usually looks better than you think it will and at this point you can clean it up a bit with your scissors.
7. After you have all your letters cut out, set them aside and lay out your banner. Put the colors in the order that you prefer. Now, if you are spelling out "happy birthday" 16 triangles will allow you to have one extra on each end and one in between "happy" and "birthday." 10 with "celebrate" will allow you one extra on the end. You really can do more or less extra - just do what you like. Take your double fold bias tape and if you are doing the "happy birthday" banner you will need to sew two packages together to make sure it is long enough. "celebrate" will only take one package. Lay each triangle in between the bias tape and pin in place. Zig zag a wide stitch down the center of the bias tape to sew the triangles in place.
9. Now, one at a time peel off the paper back of the Wonder Under on the felt letter and iron, shiny side down. It may take a few times of ironing to make sure that they are adhered.
10. If you want to add cupcakes, now is the time. I adhere Wonder Under to different colors of felt and make sure I have plenty of colors to work with. I cut them out of all different colors. I then lay them out the way I want them to look and iron them all at once -pressing down once to make sure they are at least tacked on and then running the iron over them a little at a time to make sure they are adhered all the way. Here is the template for the cupcake. I drew two (which I am sure look identical to you) because I couldn't decide which one - so you pick.
11. I don't (although I have been known to) applique with stitching the letters, but I do applique the cupcake. I do a mixture of tiny zig zags and straight stitches just to break it up and add some variety.