Step 2: Get geared up. I, like most people, get caught up in buying gear for whatever activity it is I’m into. Everyone loves buying new gym shoes or yoga pants, a new tailgate grill, fancy snow jacket, overlanding parts for the 4Runner you’ll never take offroad, ski goggles we’ll only use once… We’re all guilty of it and it can get expensive quick. But you really don’t need to buy all the fanciest of gear to start mountain biking.
Let’s start with what to wear. Do you already have some soft, flat soled gym shoes, stretchy shorts, and a t-shirt? Okay, now go back to your local bike shop and pick up a helmet. You're ready to hit the trails. If you're still only testing the waters, just buy a helmet from Walmart. If you really get into it, I highly recommend investing in a helmet from a respectable brand such as Specialized, Giro, Poc, Smith, or if you're familiar with motocross, Troy Lee Designs, Fox, or Fly.
Back to the clothing, though. I have been mountain biking for several years and just now bought my first dedicated pair of bike shorts and jersey. I run flat pedals (think about the Huffy you grew up on) and still don't own a pair of bike specific shoes like a Five Ten brand. I ride in just a pair of flat bottomed Nikes. I've been running some North Face or Eddie Bauer everyday multi-purpose stretchy shorts and a moisture wicking t-shirt since I got started.
Don't worry about clipless/SPD/whatever else is out there for pedals and shoes (remember when I said don’t get hung up on jargon?). Bike shop bikes typically do not come with pedals, you can worry about why another time. Just buy some flat pedals that you can use with an old pair of gym shoes. My bike shop actually gave me a set of pedals when I bought my bike, I’ve never changed them. You can always work your way into upgrades later.
I made the mistake of wearing my moto helmet the first few months of biking, mostly because I wanted to hold out and buy a sweet TLD helmet. That was miserable, don’t do that. You won’t need a full faced helmet unless you start going to bike park downhill trails. However, I have plenty of moto gloves that I wear religiously and I’ll occasionally throw on a moto jersey for a bike ride if I go somewhere with lots of brush. Just be practical and don’t sweat the appearance too much.
Other than clothing, you really don’t need much equipment at all. Keep the chain lubed and the tires pumped up then let your bike shop sweat the other details. I have torn down and rebuilt dirt bikes from one end to the other but the minute details involved in a bicycle operating correctly is just not something I’m willing to take a chance on.
Whether tubed or tubeless, most mountain bikes have a Presta valve instead of the Schrader valve everyone is accustomed to (a Schrader is what you have on your car). I bought a stand-up pump from Walmart that has both types built in. A small pump like this one from Topeak and a spare inner tube can be kept on you in case of emergency.
As far as chain lube, Walmart has White Lightning brand in the bicycle aisle that works great. Here’s a detailed guide on maintaining your chain from Singletracks.
You can worry about clipless pedals and shock pumps after you find out you want to keep doing this bicycle thing.
Now, last but not least: Find a trail.