With experience you'll determine how wide a lane has to be before you can stay to the right and not get passed too closely, versus controlling the full lane. If you're very near the side of the lane and you're getting close passes, look back to find a safe opportunity, and merge toward the center of the lane.

Don't feel bad if you change your mind about a particular road being wide enough to ride on the right or not. Some roads are marginal in width, and traffic conditions can change your experience. On downtown streets with more than one lane in your direction and lots of turning traffic, you'll probably find yourself controlling the right through lane all the time. On suburban arterials with 14' and wider lanes you'll probably find yourself staying to the right most of the time, merging into the center of the lane at intersections or when traveling fast downhill.

I dislike busy roads with only one narrow lane in each direction. If you stay right you are likely to get passed closely, but if you control the lane it is more likely to delay drivers due to the oncoming traffic. Do what makes you comfortable. I find these roads to be no problem in very heavy traffic that is moving slowly (I keep up with the traffic) or very light traffic (because drivers can use the oncoming lane to pass), but in between these extremes I prefer to seek alternate routes with more or wider lanes, or less traffic.

Last time I visited Santa Barbara I was impressed at the number of cyclists - far more than here in Cary, NC, where I bike commute. Most of the major roads seemed to have some extra width; the more urban downtown streets seemed quite safe for controlling the lane as long as one used good lights at night.