I have found that the more aggressive you are with drivers in busy traffic conditions, the more they tend to pay attention. As said above, tip-toeing across a lane will get you nowhere with the drivers on my commute. I look over the shoulder, give a signal, then I go. If I sort of mess around all apprehensive like I did when I first started riding in traffic, I would never get to change lanes (and would probably get run over) to boot. The drivers on my commute are some of the most backwards, redneck, ridiculous people I have ever seen (Columbia, South Carolina has the worst drivers in the US) and if I am not aggressive as well as defensive, I would not be able to make my commute.

I always signal, and I ALWAYS ride like I would drive. Take the lane when you have to, signal when you need to, follow traffic signs and signals, etc.

Always try to be more of a vehicle than an obstacle.

Joey French

i signal when it's safe to take a hand off the bars. when waiting at a light in stacked traffic i always hold the center of the lane; it sends a message to drivers not to pass until i've completed my turn movement and returned to the right-most or proper lane depending on the situation. it is also my belief that i am more visible in the center in this situation.

I think it's pretty important to try to make eye contact with the drivers if you have time and can do so safely and signal far enough in advance that they can react and slow down/let you in/whatever. I try to make sure (especially when making a left) the person behind me knows I know they're there (I look back at them) and signal to let them know my intent. Just remember that nobody is a mind reader.

I have 2 suggestions:

1. Read the PA DOT bicycle drivers manual. It will answer a lot of your questions.

2. If you can, sign up for a Effective Cycling course. It's a 3 day course (about 12 hours).
I did and I learned a LOT. I think that the course should be mandatory for adult cyclists.