Huh, I guess I've never thought too hard about this.

In the morning, the only left turn I make is onto a side street up to the office. So I usually take the entire turn lane for myself. The lane has always been empty, so I signal and make it clear where I'm headed. My left turn home is on a busy street onto a busy street that leads to a pretty congested bridge. Usually, I just go to the front of the row. I signal, and try to make it clear where I'm headed, regardless of if people are looking at me or not. Though the past few days, I've hit the light just as its turned green, so I've been able to slide on through and not worry about the oncoming traffic too much.

Edit: I feel like I have a bad track record! I've been biking "seriously" for about 2 years, and have been in 1 accident. It was ruled that the driver was to fault. Its really impressive to hear about cyclists who been at it for decades and never been in an accident!