@parmi101 honestly, it’s just practice. I know there is a straight edges method in existence but I’ve never used it so I can’t speak to its effectiveness. Just try and pay special attention to your tension as you knot.
@lizziebean for all the colours I hold the loose end in one hand and the skein in the other and pull my arms wide except for whatever colour you’ll be outlining your diamonds with, you’ll want to add extra to that as it runs out quick.