Alex in Chicago has created the best "letter to the newbies" that I've seen. I want to blatantly copy it here with attribution, but instead I'll just comment here. Please read the original text!
1. time for a check-up
Nothing like having a bike you can count on. Here in Boston I know the shops are slammed, every time I've been in I've heard people dismayed to learn that their quick fix will take over a week. The Craigslist mechanics are a great idea. I know one such outfit, two guys who are doing bike repairs in their living room in Cambridge. Email email@example.com to talk to them, and be sure to ask lots and lots of questions. As for the reflectors, Boston law says we can have a rear reflector or rear light.
2. get loaded
I love the beautiful totes and bungees end up making me frustrated. Girl, you want a basket on your bike. Every girl does at some level (depending on her bike). Give in to temptation and get a basket (I haven't yet and I really really want one!). It's a pain to carry the weight on your back. Get the weight on your bike, and if you have to bungee, so be it. You'll eventually see why I don't think that's the first choice...
3. stop being ms. nice gal
Oh, man, Alex you called it here! How hard is it, as a woman, to say "this is my place in this world and I'm entitled to it"? It can be very hard. But I know it is good for me, psychologically, every single day.
4. ignore the horns
What she said!
5. check it or wreck it
Absolutely talk to other cyclists. Road rage issues is a bond we, every one of us, share.
6. the most direct route is not always the safest
Don't think like a driver and you'll find your best way. Don't forget including all those places you keep meaning to visit.
7. slow the $%^& down
Note: cute boys will slow down if you smile, and you have the easiest opening line ever - "nice bike"...
8. it can be your fault
Set a good example for other cyclists and show cars how happy and considerate cyclists are. They'll be wishing they could lose two wheels and about 2,000 pounds.
9. they did not put ramps in the sidewalks for you
The ADA has created a problem between pedestrians and cyclists that has never before existed. Pretty please don't add to it! Just have both feet on the sidewalk, no problem at all with walking with your bike.
10. put away the ipod
What she said. I know I personally relish the "quiet" time and focus.
11. be kind to your fellow bikers
You're joining a close knit group of kind and humble people. Be kind in kind.
Alex's post is brilliant, just what I would have said. Thank you.