In order for anyone to understand what a book really meant to you - say 4 stars out of 5, then you need to explain just what those stars mean. In our case, we use the letter grade system. (A, A-, B+...etc.) We also list exactly what that grade means. For example, A = excellent, but C+ = Eh. So, readers get a general idea of what I feel about a book. There are a zillion different ways and they can be unique to you - for example, there's one blogger that does hearts for how much she loves a book. One girl does shots (her blog includes the title Tequila). Make it unique to you, or make it traditional, but either way it's great when sharing your opinion.
