Check oil twice before starting. Check oil twice when finished, with a dip-stick wipe between all checks! Clean out accumulated grass, dirt, mud, clippings under mowing deck. Keep blade-s sharp, with frequent checks. Keep upper side clean, too. Oil the wheels occasionally.
check main drive belt, if applicable, for fraying, and replace if well worn!
And, keep the blade-s sharp, too.

I would add that you should clean the mower of accumulated grass after each mowing. Not just at the end of the season.

You guys left off what I consider equally as important as oil. The air filter. Check it often and replace before it gets too dirty.

Agree. But isn't most of this stuff included in the owners manual? If so I would suggest just following the owners manual which should be comprehensive if it's a Honda.

And as I reread his message a bit more carefully he is asking specifically about the smartdrive. Smartdrive is thumb-control of belt drive slippage I believe. If so then periodically checking and adjusting the drive belt clearance would be a good idea.