Ok, here is a quick guide.
Loosen all straps completely.
Put the headset on your head, front to back, like you were putting on a gasmask. Most people put it on like a baseball cap.
Make sure the triangle of straps at the back of the headset is as low as possible on your head. Almost to the neck.
Now tighten the side straps, don't tighten them too much, just enough so that the headset isn't loose on your head. Over tightening makes things worse.
Now tilt the faceplate until it's comfortable (more people don't realise that the faceplate moves)
Then tighten the top strap. Tighten it until it takes the weight of the headset but not too much so that it moves the headset from it's current position.
You will know when it's right because the headset will feel much more comfortable. Most people get headset face because they are using the side straps to pull the headset into correct position and this means the whole weight of the headset is on the face.
If these are unclear, let me know and I will go look for the proper instructions