Before I got onto the start of the path in Back Bay I was yelled at to "get on the sidewalk" by a passing car full of young intellectuals. I fumed for about 15 minutes, thinking of what I would say next time, then forgot about it once I got to the park.
Anyway, I wanted to share "the rules" according to MassBike, a Federal Highway Administration program. Sorry if this is old hat to some of you. I think it's new hat to more of us than care to admit.
Give Yourself Some Space: You’ve got a legal right to the road, so use it – take the full lane when needed, stay away from car doors, and don’t squeeze between lanes. Two bicyclists can ride side-by-side, but get into single file if cars can’t pass safely.(more)
Go With The Flow: Ride in the same direction as other traffic, and ride as straight as you can, don’t weave between parked cars or into crosswalks.(more)
Take A Break: Stopping at red lights and stop signs gives you a chance to relax, chat with the cute biker behind you, and set a good example for everyone one else on the road.(more)
Light Up The Night: Lights help you see where you’re going, but it’s more about everyone else seeing you.(more)
Walkers Go First: If you run into a pedestrian, it doesn’t matter who was right or wrong, it just hurts.(more)
Get Some Head Insurance: We hope you’ll never need your helmet, but the one time you do, there is no substitute. Your brain is your most important piece of safety equipment.(more)
And for the motorists (that's probably all of us):
Bicycles Are Vehicles Too: The law says bicycles are vehicles, and it’s OK (and often safer) for them to ride in the middle of the lane. (more)
Bicycles Reduce Traffic: Sometimes it might seem like bicyclists are slowing you down, but remember every person on a bicycle is one less car on the road. (more) OR TAKING YOUR PARKING SPOT (my addition)
Save The Squeeze Plays For Baseball: Stay a few feet away from bicyclists when passing - don’t try to squeeze past them. (more)
No Sudden Moves: Abrupt turns can cause crashes, so always look for bicyclists and use your turn signals. (more)
Look Before You Leap (Out): Look behind you for approaching bicycles before opening a door on either side of your vehicle. (more) There's a $100 fine for doing this! I did this to someone once, it was terrible. She fell off her bike and dropped all her groceries.
The Truth About Bike Lanes: While cars must stay out of bike lanes, bicyclists do not have to stay in the bike lane. (more)
There’s No Nice Way To Honk: Honking can startle a bicyclist and cause a crash, so only honk when absolutely necessary. (more)
That's all straight from the MassBike website, so go visit them if you want more info. I hope this is a helpful start!