One thing I want to do in the new year is to take more double exposures. I think it's funny that I almost always prefer my accidental double exposures to my intentional ones.
There are not a lot of cameras which both make it easy to avoid unintentional double exposures but also easy to intentionally make double exposures. Large format cameras and simple box cameras usually make it too easy to double expose. Most 35mm cameras are difficult to double expose, requiring one to rewind one frame. The Nikon FM and FE are probably the best balance between the too. I need to do some medium format double exposures with my Yashica D or a Holga too.
Metering for double exposures is quite easy, just underexpose by one stop for both shots. One usually needs to boost the contrast at the end though.