You need two kinds of triangles:
The corners are made using TWO squares, cut corner to corner. This puts the grainlines on the outside edges and the bias is attached to a grainline. This stabilizes the bias and keeps you from having a bias on the outside.
The other triangles are made from squares cut into 4 pieces, corner to corner. This puts the grainline on that outside edge, and your bias edges are attached to interior blocks that stabilize the bias.
Bottom line: You want grainlines along the outside edge, and you want bias edges stabilized by attaching to blocks that are on grainlines. If you have bias on the outside edge, you WILL end up with what we call friendly borders: they will wave at you. I'll go see if I can find a link that helps you figure out the sizes.