Motion becomes believable when speed changes feel intentional. Good easing is not decoration added at the end; it is part of the idea from the first keyframe.
Read the movement without effects
Temporarily disable blur, texture and secondary animation. If the main action feels weak in a simple preview, additional polish will only hide the problem.
Check the reason for every acceleration
Objects should speed up or slow down because of weight, force, attention or narrative emphasis. Avoid using the same curve everywhere simply because it looks smooth.
Protect readability
Typography and interface motion need enough time to be understood. Pause on important information and test the sequence at actual viewing size rather than only inside the composition window.
Compare adjacent movements
Transitions feel connected when the outgoing energy informs the next action. Look for awkward stops, competing directions and moments where everything moves at once.
Review at full speed
Looping a tiny section can distort your sense of timing. Watch the complete piece regularly, with sound, and note only the moments that pull attention for the wrong reason.