This is a good one after you think you have your library rated the way you like it, but imagine there may be a couple hundred songs hiding in your 3 star list that need to be "reconsidered" as 4 or 5 stars.
Create a playlist:
Rating is 3 stars
(or whatever the bulk of your music is listed as)
Last played is in the last 3 weeks
(or whatever, something recent)
Limit to 100 songs by most often played
This creates of list of your middle-of-the-roads that you have been listening to more than you think and should probably move up in rating.
You can also introduce a minimum number of playcounts.
Can use same rationale and analyze the higher rated songs, instead looking for least played in a long amount of time (3 months+), creating a list of those that you probably keep skipping past and should downrate.