At least if he or she is working in the fields of the historical or fantastic:
- Fire a rifle or handgun. If you don’t have the sort of friends who own firearms and back pastures where they can set up tin cans on fence posts, visit a shooting range. (But the effect of a bullet on a full tin can of dubious green beans or corned beef hash is a lot more impressive than holes in a paper target.) If you’re working on stuff set in the black-powder era, see if you can find a black-powder enthusiast for a demonstration.
- Build a fire starting with tinder and matches. Starting with flint and steel, or with even more basic gear, is rather more hard core than necessary, though if you happen to know a Boy Scout or a historical recreationist who’s into that sort of thing, you should take the opportunity to observe the process if you can. It explains, among other things, why so many fictional wizards keep a handy firestarting spell in their back pockets, and why the ancient Romans were so big on keeping a fire burning in the Temple of Vesta.
- Try on some armor and a helmet. Cultivating the acquaintance of some historical recreationists, again, is good for this. You’ll most likely end up in chain mail, because plate armor is a lot more size-specific. But the narrowed field of view and dampened sound inside a closed helm are certainly instructive.
- Wear the clothing of another era, for insight into how movement and demeanor are affected by it. What can and can’t you do in hoop skirt and corset, for example; or in high heels, a powdered wig, and a sword?
- Cook and eat a meal from the same era. Bonus points for doing it over the fire you started with tinder and matches.
- Get far enough away from major urban areas to see the night sky unaffected by the glow of city lights, and hear the world without the background rumble of machinery and hum of electricity, and smell the world without the overlay of internal combustion engines and industrial processes. You don’t have to stay there; just visit it for a few hours, or a day or so.
And that’s just for starters. Not all research is done in books.