Ignoring the chain. By far the most common form of neglect, almost every bike I have got in for service in my half century of at this has suffered from having no attention paid to it at all. Seriously, folks. What is up with that? The drive chain on a 70s Honda four needs looking at every 200 miles. Obviously, the chain won't need adjusting every time, but it definitely will need lubing, and fairly often also adjusting.

Adjusting the chain too tight. Those not educated in proper maintenance make this mistake almost universally. Look at the swingarm. Note that it is not level with the floor. This means as the rear suspension is compressed the swingarm will rise toward being level, and when it does, the chain will tighten. This is because the pivot points of the swingarm and of the chain are not at the same place. If they were, the chain's tension would never change with suspension movement. But they aren't and so they do. The chain tightens when you sit on the bike. It tightens some more when you go over a bump. Therefore, you must allow slack in the chain when the bike is on the centerstand that will accomodate this tightening. If you don't, the chain will be overstressed and so will the transmission. I once saw a transmission bearing fail due to this.

Lubricating the chain incorrectly. It amazes me that this late, after this many years in powersports history, and with so much information available, almost no one knows how to lubricate a drive chain. I know this because I see a lot of bikes with chain lube spattered onto their wheels, fenders and elsewhere. And I see even more-- virtually all in fact-- with perfectly dry chains. With the machine on its centerstand, and preferably after a ride when the chain is hot:

1. Point the hose of your aerosol at the juncture between the side plates. The chain has four side plates horizontally making up a link pair, with a roller separating the plates. Lubricate between the first two plates, and when done move to the last two plates.
2. Lube the chain on its inner run, not on its outer run. This way centrifugal force will coax the lube in-between the plates and little if any will fly off. Do not lube the rollers and do not lube the sprocket. That wastes lubricant and makes a mess.
3. Then check the chain's slack. About every fifth lube, a tiny adjustment will likely be needed.
4. Again, do this often; count on every 200 miles on the CB500/550 that uses a non-o-ring type chain.