I found a quick way to cut lots and lots of triangles from the same fabric:
Square up the end of the piece of fabric. Now square up the other end, too, and lay them on top of each other, with the cut ends facing you. Cut three or four strips, but don't touch the strips after you cut them. Leave them where they lie.
Cut squares the other way, the same width as you cut the strips. Leave them where they lie. If they move a little, just nudge them back where they belong.
Now lay your long ruler on the diagonal, making sure the ruler is going through each diagonal all the way up. Cut on that diagonal line. Cut all the diagonals that way. (Not both ways.)
You can pick up your triangles in groups of four and have them ready to "deal" out to line up your pattern, and you're ready to sew.
If you cut strips 3 1/2 inches wide, cut the squares 3 1/2 inches, too. You get 6 squares from each strip. Each square yields 8 triangles. That's 48 triangles from each strip. How many do you need? Make that many strips. I wouldn't make more than 4, as the diagonal cuts would get too long. That's from a piece of fabric WOF X 14".