The quality ratings are purely objective and can be based on a number of factors. Here are some tips to increase your rating: 1) Increase the number of claims. 2) Decrease the length of each claim. 3) Increase the length of the specification.4) File patent as a continuation or CIPs.5) Vary the type of claims. 6) Cite more references in your IDS.7) Cite non-patent references or foreign patents.8) Limit patent prosecution history.
FYI: U.S. Patent 5,583,591 has been identified with an A+ rating.