The One Thing You Need To Know

To climb rocks: Use your feet. Despite what you may have seen in Cliffhanger, or depictions of climbing in energy drink ads, rock climbing is is less about doing 40 pullups in a row and more about techniques that place your weight on your feet and reliance on core strength.
Another thing: If someone yells “rock,” duck, don’t look up. You’re trying to avoid a falling object, not catch a foul ball at a baseball game. If a small rock, a cam, a carabiner, or a large rock comes flying down from above, catching it with your face is probably going to ruin your day.

To boulder: Every fall is a ground fall
Another thing: It’s perfectly acceptable to spend half of a day (or an entire day) trying to climb eight feet of rock

To climb ice: You’re not doing it because it’s comfortable: it’s cold, it’s wet, you’ll spend lots of time standing in snow, chunks of ice will come flying at you from above, your hands and feet will go numb, and that’s just when you’re belaying. When you’re climbing, you’re attached to several sharp points capable of ripping your clothes and/or flesh, and when you get to the top of a pitch of ice, you’re likely to experience something called “the screaming barfies,” a pain from rapidly warming hands so named because you will want to scream and vomit at the same time.
Another thing: It’s pretty fun if you’re into that sort of stuff

To camp: In a tent, you will probably not sleep for eight hours straight like you do in your bed at home, but if you get good at camping, you can get five or six somewhat consecutive 90-minute naps
Another thing: Other animals in nature also enjoy food, so don’t leave yours out overnight or when you’re away from your campsite. Squirrels can ruin your supply of snacks, bears can ruin your life.

To go backpacking: An oft-cited adage says, “ounces equal pounds, and pounds equal pain.” When you’re at home piling up all your stuff to pack for your trip, that paperback/French press/extra change of clothes may seem like it’s worth it, but three miles into an eight-mile hike with all your stuff on your back, it may turn into the bane of your backcountry existence.
Another thing: Don’t ever share a tent with anyone who says “they don’t really snore”

To hike: Hiking is pretty much just walking on dirt and rocks, so you don’t need a lot of specialized skills to do it
Another thing: It’s different from walking in that you can get caught in a thunderstorm, get lost, and have unexpected things happen on the trail, so it’s not a bad idea to buy a rain jacket, a map, and a headlamp, and always let someone know where you’re going.

To mountain bike: Even a very slow mountain bike crash can be really painful
Another thing: You don’t need an $8,000 mountain bike to get started (but they sure are fun)

To ski: Taking a ski lesson may seem expensive when you’re first starting out (in addition to lift tickets, equipment, and ski clothing), but think of the money you spend on it as an investment in fewer shitty ski days in your first season—you’ll learn and get better way more quickly, and will spend less time flailing on the slopes your first 10 times.
Another thing: Skiing fast doesn’t necessarily mean you’re good

To ski in the backcountry: As the saying goes, “The avalanche doesn’t care if you’re an expert.” Also, the inverse: The avalanche doesn’t care if you are blissfully ignorant of what causes avalanches.
Another thing: There’s no ski patrol in the backcountry

To snowshoe: Don’t try to walk backwards while wearing snowshoes
Another thing: It’s really just walking, in snow, with big things on your feet

To flatwater kayak: Push the paddle from your core, don’t pull it with your arms
Another thing: It’s a lot easier to stay in a boat than to get into a boat after you’ve flipped it

To trail run: It’s usually slower than road running (i.e. it’s not just you), unless you’re on a perfectly groomed, flat trail (which a lot of people including myself would say isn’t really trail running)
Another thing: Rocks and roots may be taller than they appear

To SUP: You can also sit and kneel on a SUP board, if that’s more comfortable at first
Another thing: If you haven’t SUPed before, SUP yoga might have a pretty steep learning curve

To bike tour: The slower you go, the more fun it is. Trying to hammer out as many miles as possible on a fully-loaded bike is a recipe for burning out. It’s a tour, not a race.
Another thing: Take care of your butt and it will take care of you

To bikepack: With a fully-loaded bike, there’s no shame in getting off and pushing it up hills
Another thing: Bikepacking is just bike touring on dirt. Or bike touring without panniers. I think. I don’t know if anyone actually knows. Also, take care of your butt.