To me, a good draftsperson should have:
-Familiarity with the technical details of what is being drafted, associated codes, etc.
-General drafting knowledge and familiarity with blueprints
-Drafting standards of the particular employer, including abbreviations, weld symbols, etc.
-Familiarity with other similar work done by that employer
-Details of the software to be used and how to efficiently use it
-Reasonable math skills, which for tanks involves using trig functions, arc lengths, coordinates, etc.
-Some artistic ability
-Speed
In my experience, not too many draftsmen have ALL of those characteristics.
Probably items to work on
-Getting familiar with past work done- most drawings are generated by pulling up something similar and modifying it as needed, but you have to know to look for it, too.
-Getting familiar with applicable codes (API-650 or whatever). If your employer uses software for the design, get familiar with the output of that software.
-Getting familiar with the basics of the software. Common issues I see are not knowing how to make all the text in a drawing the same size, not knowing how to make linetypes print as they should, etc.