Never, never ride against the traffic. I take the lane to make lefts, get into the traffic a good distance ahead of the turn and stick my arm out. My friends make fun of me because when I'm signaling, I sort of shake my finger/hand to emphasize I'm turning. They say it's my school teacher scolding signal. I feel much safer in a line of cars as they usually give me a wide berth, rather than being pushed to the side of the road. I will get in a line of cars when going straight at an intersection, if I think there's a narrow space on the right. My husband on the other hand, rides right up along the cars in teeny tight spaces in horrible traffic. I can't do that!
I have gone up on a sidewalk a couple of times when I was at a very busy spot and saw that I couldn't get in the lane to turn. I stopped and then went straight across the intersection. However, there aren't sidewalks around where I live in too many places, so this really isn't an option.