Learn right away that the front brake is the most effective one, and to never lock the front wheel in dirt.
Learn how far you can lean over without scraping a pedal.
Learn to keep the inside pedal UP when you corner, and learn to ride safely in all conditions.
Signal your approach to pedestrians, especially if they're old, and a bell is better than a shout. If no bell, try clacking your brake levers. If all you've got is your voice then that's fine.
Signal your approach to pedestrians, especially if they're old, and a bell is better than a shout. If no bell, try clacking your brake levers. If all you've got is your voice then that's fine.
At least one ride in 10, go without your sunglasses and gloves.
Sometime next month, put some double-sided cheap-style pedals on a good bike and ride in non-cycling garb.
Carry an extra tube you can donate to somebody with a flat tire and just a repair kit.
Don't try to be a mentor to every cyclist you meet. 
Don't ride in shoes you can't walk through an antique shop in.
Don't ride in shoes you can't walk through an antique shop in.
Don't wear clothing that makes your sweat stink even more.
Don't think you'll go faster in a significant way if you and your bike become more aerodynamic.
Put a $20 note inside your seat post or handlebar and hold it there, somehow.
Don't ride until you're confident you can fix a flat.
If you ride more than one bike, have a set of bring-along tools for each one. Learn how to remove your rear wheel (put the chain onto the small cog, etc.).
If you ride in a group, bring food for you and somebody who forgot to.
Go for a one-hour ride underdressed sometime, because it's good to be really cold on a bike every now and then.
Never blame your bike or your health or anything else if you're the last one up the hill or in to the rest stop.
If your brake hoods are black, wrap your bars with a different color tape.
Never let your chain squeak.
Never let your chain squeak.
If you pass another rider going up a hill, say more than "Hi."
If you see another rider approaching you from the rear, trying to catch you, let it happen. Fun is more important than fast.
Sometimes, bring normal food on your ride.
Shoot photos on your rides and give them away.
Feel comfortable mixing high tech and low tech, old and new parts and technologies, and don't apologize to anybody for it.
Compliment other people's bikes, especially if they're new.
Buy the cheapest helmet that fits well.
Don't always shop by price and never ask for discounts at your local bike shop. Every time you go into a bike shop, spend at least $2, and if you ask a question and get good advice, spend $5 (get a cable).
If you buy a rack, don't ask for free installation.
Don't assume your bike shop is making money.
Ride only when you feel like it.
Have at least one bike you feel comfortable riding in a downpour.
Ride in weather that keeps other cyclists indoors.
Never keep track of your pedaling cadence.
If you have a normal loop or ride, count the number of times you shift on it; then the next time you ride it, cut that in half and see if it makes any difference.
Learn to ride no-hands and to hop over obstacles, but not simultaneously.
Never hit a pedestrian. In traffic, be visible and predictable.
If you have several bikes, set them up with different equipment but always ride the saddle you like best.
Don't try to keep up with faster descenders if you're not comfortable descending.
Never apologize for buying something that's not quite pro quality by saying, "I'm not going to race or anything."
If you buy a stock bike, do something to it that makes it the only one exactly like it in the world.
Don't think it's important to match front and rear hubs or rims.
If you borrow somebody else's bike, for a short test or a long ride, say something nice about it.
Always bring a pump.
Build at least one wheel.
Wear out something.
Don't ever describe any bike, no matter how inexpensive or dilapidated, as "a piece of crap."
If you get a fancy bike assembled by somebody else, allow them a scrape or two, especially if the bike is really expensive.
These tips (slightly edited) are from Rivendell Bicycle Works
And I would add "Love your Bike!"
