A diagonal arrangement can help a thumbnail communicate movement, especially when the video demonstrates a tool or a physical process. The direction should come from the action itself rather than an arbitrary tilted frame.
Follow the working line
Look for the natural path of a hand, blade, brush, or object. Frame that line so it remains visible from one end to the other. In a painting demonstration, the brush and the area being painted should form a readable relationship.
Stabilize the surroundings
Keep supporting elements quieter so the diagonal does not become visual noise. Avoid tilting every object or adding unrelated slanted text. One strong direction is usually easier to understand than several competing ones.
Check the crop
At small size, confirm that the hand still connects to the tool and the tool to the task. A dramatic crop that removes the contact point can make the action ambiguous. Choose clarity first, then use the diagonal to reinforce it.