Applying thermal paste is super easy but some folks made it complicated. Saw a test recently where the paste were applied in different ways like: put an X-shape, put a pea size blob, put a straight line, put a rice size blob and even draw a smiley face. Actually all worked! At the end they measured the temperatures and the difference was only 0.5 to 1.4 Celsius.
Nevertheless one can find many many pages on the net about how one should use only the x-shape or use a card to even out the paste and how a card should not be used...etc.