Congratulations on bike-commuting.

Perhaps you might convince a friend or coworker to bike with you: two bikes are easier to see than one. Also, I recommend going at about the same time every day: that way, the people who drive along that route every day at the same time will get used to a bike being on the road.

As for left turns, I judge it by the road and how comfortable I feel.

Do you have showers where you work? I sometimes shower right before I leave, and then my sweat isn't as smelly as it would have been if I hadn't showered. But usually I like to shower at work. I've read that one person brings a washcloth soaked in water and ethanol in a baggie and uses that to wash the smelly parts when he gets to work.

I also recommend bringing a spare tube in your pannier (I heartily recommend panniers over backpacks). When you get a flat, it's a lot nicer to just switch out the tube and deal with repairing the hole later.

I'm looking forward to all of the great advice others will have : ).

-Sara-