Note that I live in a heavily forested area of the Pacific Northwest (in North America) so not all of this may apply to you!
Please be mindful of animal parts laws. Not all bones are legal to possess.
Also know the laws and regulations in the area you’re searching. Who owns the land? Is it a protected area? Can you legally take anything from it?
Animals (such as rodents) use antlers and bones as a source of nutrients. How impactful will taking the bones you found be to them? I ask that you hold some awareness and do what feels best, even if it means leaving the bones behind.
Where to look (casual version):
Under bridges, you’ll often find owl pellets with rodent and bird bones in them.
If you see hairy scat (poop) get a stick and break it apart, sometimes there’ll be small animal bones/bone shards. Please be safe, predator scat can have icky things like parasites.
The sides of trails. I’ve found so many bones there!
Driving pullouts that are a bit private, if you feel okay with using bones from roadkill/poached animals.
Along railroad tracks, unfortunately many animals get killed by trains.
Where to look (dedicated version):
A few feet to 10+ feet into the bushes past a meadows edge.
Go to the big trees, animals are drawn to them.
Check out holes in the ground.
The sides of back roads/logging type roads.
Explore the parts of the forest you haven’t been to before. Make new trails. Walk along fallen logs.
In strangely clear spots in the forest. (As I’m editing this post, i see this and realize that’s exactly how I found a skull today)
Crawl. I’ve found so many bones by just crawling around (usually looking for other things/checking stuff out).
Go where you feel drawn to. What areas stand out to you?
DEER. TRAILS. They take you to less humanized areas easily.
I mean really, whenever you want. I’ve found bones every time of year and every type of weather, but some times tend to be more fruitful than others!
After spring thaw, heavy rains, floods, or freezes. Weather changes can either push up and expose the bones, or remove a layer of leaves/soil/snow that kept them covered.
Think about what lighting will make the bones “pop”, or have the best contrast with the terrain around it. In my experience, overcast or indirect light it best.
Rainy/wet days can also help because they make the bones more shiny—especially in forested places where they normally are camouflaged color-wise with the forest floor.
Bones can often get spread out, but where you find one you can typically find more if you look far/ wide enough.
If you live in a foresty type place, bones are rarely bleached white. Look for browns, greens, mild whites that don’t quite look like sticks.
Skulls aren’t always in same area as the rest of the bones because it’s a good food source for animals so they’ll drag the head off for themselves!
Think about where animals would go to die.
Learn the killing/feeding behaviors of the predators in your area. Where do they hunt? Where do they like to eat? (And make good choices. If you put in the dirt time you will start finding killsites and not all of them will be old).
You won’t always find bones! Some places just don’t have any! Some have bones that are buried.
This certainly isn’t all-encompassing, and I’d welcome people in different regions to jump in with their methods :) I wrote this while living West of the Cascades in the PNW.
On using bones in witchcraft
Animal parts laws (external site)
Book recommendation: (animal skulls)