First Diagonal Fold for Paper Airplane
We are ready to begin making our plane. For the first fold, you want to have the paper oriented in a portrait style vertically. And, if you're left handed you start with this corner and bring it down. If you're right handed like I am, take the top right corner pull it until the left edge is flush. You will then keep that straight with one hand and run your finger along this forty-five degree angle to the corner.
Make sure the creases are very sharp. Go over it a few times with your thumb if you want. Or, with the palm of your hand to make sure it's sharp and there's no air between.
So, again we take the top bring it down to here so it makes a forty-five degree angle with a rectangle at the bottom. And, that's the first fold.