V-brake rubs on one side, then the other
 

I adjust my v-brake so that neither side rubs. The next day it starts rubbing on one side, so I adjust it so that it stops rubbing. Then the day after that it starts rubbing on the other side. So I adjust it again and then a day later it starts rubbing again on the side it rubbed on two days before. And so it goes on in an endless loop. How do I fix this?

Maybe take the brake arms off the posts, clean the bearing surfaces up, regrease, and reassemble. It's fairly easy.

I like V-brakes but they can change their mind quickly. It seems that whenever I undo them to remove a wheel, they never center the same and I have to mess with the springs.

Any time I adjust them I squeeze the brakes a bunch of times before I call it good.

Thanks for the tip. Could I use vaseline as the grease? It's the only viscous lubricant I've got in my apartment.

Yes.

It's better than nothing.
Petroleum jelly.
It probably won't last as long as a "dedicated grease", but it's not like an axle constantly rotating.
It's good enough to see if lubrication is the problem.

You might try disconnecting the springs from the arms, bending them out so they push out harder, then putting them back. You'll need some trial and error to get the spring tensions approximately equal. I've done this, and it works. But yeah, V-brakes are annoying in this way.

Does it "switch sides" depending on how quickly you release the lever?

A problem I had with v brakes once was that, as they wear they are moving in an arc, this makes them move slowly downward on the rim as the wear progresses, after a while a portion of the pad is no longer in contact with the rim and develops a lip. This lip can catch on the rim causing them not to release properly. This and has been mentioned brake posts with no lube and cabling have caused most of my v brake issues.

Yep,

I use fine steel wool on the bosses and a .38 caliber brass gun barrel brush inside. Once all nice and shiny, lube and reassemble, work's like new:)

Usually if i need to tighten an adjust screw - i'll loosen the other side. (depends)

Are you sure that the locknut and cone on your wheel hub has not worked loose? Make sure there is no play in the hub when the wheel is affixed in the dropout, as this can make it seem like the brakes are coming out of adjustment when the wheel 'wobbles' back and forth due to the play in the hub bearings.

The bending of the spring is one way to increase tension, and if that doesn't do it, assuming your frame has different holes on the brake mounting post, change the hole position to increase tension.