first: what do I really feel like doing? do that
if nothing in particular, consider some big picture thing I care about, then see if anything arises that I want to do
if still nothing in particular, consider if there's anything that benefit strongly from being done sooner, such as booking appointments or applying for something that will take awhile to process
if nothing time-sensitive, take care of some business that I'll need to take care of eventually, like filing my taxes or throwing out some moldy food