Advice Need Advice: Driving in North and South Wales

I've visited Wales twice before, but my relatives always arranged trains and buses for me. This time, I'm considering renting a car to explore more freely. I'm a bit nervous about driving there, though. How are the roads in North and South Wales? Are there any specific challenges or tips I should know about? Also, any recommendations for scenic routes that are manageable for someone not used to driving in the UK?