I've taught lots of first-time adults. It's definitely more challenging than teaching children. Every adult will come to cycling with a different background and different fears. If someone has an athletic background, especially balance sports (skiing, skating, gymnastics, etc) it is usually much easier. Embarassment is a very real factor for many new adult riders, so try to be sensitive to this. And don't push too hard too fast. Learning takes a lot of mental energy which is exhausting. Let your friend succeed at one part of the learning process and then stop and come back for another session to move onto another part of the process.

First, check to see if there are any classes in your area. Let someone who knows what they're doing teach your friend. This would also reduce the chance of "strain" in your friendship. Good instructors know all the tips and tricks too.

Training wheels are a bad idea. I think they're a bad idea for children too, but that' another thread.

I do, however, recommend that learners use protective gear if they're at all aprehensive of falling. Elbow, knee, and wrist guards will instill some confidence and make a learner feel safer. And, of course, don't forget a helmet.

Here's how I typically approach teaching a first-time adult:

  • Find a quiet place with few distractions. Try not to go to a very public place like a park where your friend might feel self-conscious.
  • First, lower the saddle a bit. You want your friend to be able to put both feet firmly on the ground while sitting on the saddle. I don't recommend a bike that's too small (as others have said) -- that will affect handling and balance.
  • Now, just see if your friend can do it. Sometimes it takes very little teaching -- some folks are just naturals. Explain the basics -- look where you want to go, push off at the top of the pedal stroke, etc.
  • If this doesn't work, advance to plan B -- scooting. For this, I will sometimes take the pedals right off the bike. This allows the rider to scoot the bike under their own power without hitting their legs on the pedals. Scoot, glide, stop, and repeat. You can also do this on a slight grassy downhill (very slight). The grass is softer if their balance isn't good and the downhill will give them a little momentum. As you know, balance on a bike is easier with a little bit of speed.
  • Once your friend can scoot and glide, put the pedals back on and see if she can shoot and glide while balancing her feet on the pedals. After she feels comfortable with this, teach her how to pedal.
  • Until someone is comfotrable pedaling on a flat straight road at 8+ mph, don't worry about teaching how to turn or corner.