If you want to make cool rockets, just build you basic rocket first.
Next, make sure the shape is aesthetically pleasing. (Nice to look at.) Then take your fuel tanks and texture them, breaking them into smaller tanks of the same width to add detail. You could also just keep them nice and clean looking, but if thats the look your going for I would try and make your whole rocket sleek and cool looking.
If you want pipes or fuel lines, use part editor or BP editing to make fairings very thin and add them. I recommended trying out different shapes and configurations to try and get a rocket that looks nice.