One of the posts I read recently is Grant's Tips for Happy Riding. It's golden. You can click through and read the original or keep going and read my edited version below.
Your bike does not have an anti-lock brake system. Truth: the front brake is the most effective one. It can also get you in trouble if you mis-use it where traction is dicey. (The rear can get you in trouble, too.) When braking really hard, shift your weight back on the bike as much as possible.
Learn to ride within your skills, and prevailing conditions.
Consider whether you really need to ride narrow, hard, fragile tires prone to pinch-flats and punctures. Consider riding larger volume tires for comfort, safety and fun.
Get a bell. It's a friendly, cheery way to announce your presence, and everybody knows that bell means bicycle.
Stay away from pedestrian paths whenever possible - especially sidewalks.
Occasionally take a shortcut, even one that requires riding on dirt, or even walking.
Try riding without toe-clips, or clipless pedals. Ride in comfortable street clothes once in a while (or even usually).
If you ride more than one bike, consider setting one of them up as a single-speed - especially if it's a drop-bar road bike. You'll be surprised at how it changes some of your favorite rides.
Carry an extra tube to give away to somebody with a flat tire and just a repair kit. If you see a cyclist at the side of the road, ask if they need anything.
Don't ride in shoes you can't walk in.
Old, steel bikes can be just as reliable and comfortable as new expensive ones made from 'unobtanium'. Sometimes older bikes can be even more comfortable, and more fun than a newer steed.
Don't think you'll go faster in a significant way if you and your bike become more aerodynamic.
Put a $20 bill inside your seat post or handlebar and hold it there, somehow.
Once in a while go for a ride after dark. Take whatever precautions you feel are safe, but get out there in the dark - it can be really fun.
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. Make sure your tool kit includes a tool for every fastener on the bike. Learn how to remove your rear wheel (put the chain onto the small cog, etc.).
Don't be a weight weenie. Better to take weight off your middle than your bike.
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. The reverse (overdressing in hot weather) is not necessary!
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.
Never let your chain squeak, or your brake shoes squeal. Learn how to maintain and adjust your bike!
If you pass another rider or are passed, be friendly, say more than just 'hi'.
Set your bike up for comfort. Don't worry about fashion.
Don't hit on other cyclists. Be friendly, not predatory.
Unless you're riding a marathon-class event, bring regular food on your ride (in lieu of sports bars or sticky goop). Sandwiches! Fruit!
Shoot photos on your rides. Post them to your favorite social medium.
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. [I have to comment on this one. While I realize that it's irresponsible and dangerous to suggest anyone ride without a helmet, I think Americans are overly obsessed with them. 98% of all the bicyclists on the planet ride without helmets most of the time and don't suffer for it.]
Try seersucker shirts for hot weather riding, and long-sleeved ones are best.
Never underestimate the power of fig bars.
If you get a new widget and like it, don't "swear by it."
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 $5, and if you ask a question and get good advice, spend $20.
If you buy a rack, don't ask for free installation. In fact, don't ever ask for free installation - respect your bike mechanic, don't try to take advantage of him/her.
Don't assume your bike shop is making money.
Ride only when you feel like it.
Wool is the miracle fiber. Consider wearing old Pndleton shirts in lieu of expensive italian wool jerseys - you'll be amazed how comfy they can be.
If you know a fast new rider, don't say, "You really ought to race."
If you see a stocky woman rider, don't suggest she race track.
Have at least one bike you feel comfortable riding in a downpour.
Ride in weather that keeps other cyclers 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 polite. Don't feel as though you must be a role model for all other riders; be polite for selfish reasons.
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.
Learn to build a wheel, clean a chain, adjust and lube your bearings.
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.