Make gradual changes and you'll gradually become more confident.

If you work out a regular route, you may identify bits that are awful, and then you'll figure out ways to avoid riding on the awful bits.

There's one stretch of my short work commute where there are 3 lanes, eastbound (blinded by the sunrise in the morning), 40mph limit (which means everyone drives 50), no shoulder, and one of those wacky, tire grabbing cliffs where the re-re-repavement meets the gutter.

I rode that exactly one time, felt lucky to have survived, and now have a clever way to avoid it.