always only ride as far to the right as is safe to fairly share the road with faster vehicles wanting to overtake. Cyclists in Texas have the right to claim narrow lanes for your safety, but also cannot knowingly disregard the safety of other road users by impeding traffic without cause. This was a recent appelate court decision regarding bicycling in texas that should regulate your riding somewhat.
Everyones positioning advice is sound, the mirror advice is what i give cyclists getting started with commuting. I'd also recommend a bright front array, a high powered LED for daytime visibility.