Cut your piece of patterned paper or cardstock to the required length and width.
With the RIGHT side facing you gently bend the two outer sides together.
TIP - be light handed - you are merely holding the two sides in place not folding them together.
With your scissors cut on the diagonal from the bottom right corner across the desired width.
TIP - the wider the cut, the deeper the notch.
Hey presto - one equally spaced, non lopsided banner.
and here it is used on a card I did for UnstampaBelles.