The arms are usually fairly well seated in the sockets, and don't tend to come loose unless you repeatedly pull them out, however I've certainly got some older minifigs with very wobbly hip joints. I don't remember swapping legs/hips as much as arms as a kid, so I'm reasonably confident that those are more "wear and tear/aging" than the arms.

Both arms and legs are held in place through a fairly simple compression pin.

A small dab of washing up liquid applied to the joint should lubricate it quite well - avoid oils as they can cause discolouration of the plastic.

If that doesn't work for you, then you could try physically loosening the pins - gently pull the arms out of the sockets and the legs off the hips and replace them a couple of times - this is usually enough to compress the arms of the pin enough while still maintaining a grip on the part. Going further you can obviously compress the pins manually and fairly permanently - however this will likely make the joints too loose for your needs - I've certainly got some older minifigs with very wobbly hip joints that can no longer stand up on their own.