Actually, leveling might not be the whole story. I've had nights where everything was perfectly level, but Mars still looked like a blurry orange blob. Atmospheric turbulence plays a huge part, especially for planets. Last week, the seeing was so bad that even with a solid setup, details were mush. Sometimes it's just waiting for the right moment when the air settles down. A level base helps, but it's not a magic fix for every blurry view.
@charlie_allen mentions atmospheric turbulence, but a level tripod is still crucial. Without a solid base, even clear air won't give sharp views. Fix the setup first, then blame the sky.
Remember the time I spent an hour leveling my tripod on a brick patio, only to have Saturn look like a wobbly potato through the eyepiece. I was so sure I'd nailed the setup, but the air was just soup that night. Felt like a real fool blaming the gear when the sky was the problem all along. Now I just laugh when I get everything perfect and the planets still dance like they're at a rave.