I'm no expert in this area, and I've heard that search engines can be very unforgiving when you try to change or restructure things in certain ways. What should I definitely NOT do? Are there certain things that are wrong but are better left unoptimized if I already have a high page rank?
Below are some points that are the black hat techniques If you have applied any one of these then remove them other wise just keep on building the quality backlinks for you website. and congrats for having the high page rank.
Yup, and if you are ever wondering whether or not to undertake a particular strategy, ask yourself if it adds to your users' experience.
A few notes: if you are changing domain names make sure your redirects are done properly. Always be aware of potential duplicate content, and I would advise to leave pages with high authority alone. Look at your Analytics tool to see which pages are your most important landing pages and don't mess too much with those.
Better leave robot.txt file part, and don't think of making a keyword rich content, write naturally. Consult an internet marketer for link building.