It has been a long time since I systematically watch animes. Now I watch them purely at whim. In the future I might finish some famous titles.
General rating rules:
If the anime shows some effort to explore some rather deep issues, as long as it is decent I would probably give it at least 7. In particular, movies (that I watched) tend to score high mainly because of this reason. For slice of life or animes purely for light enjoyment, their score typically ranges from 5-7.
There are of course exceptions to this. For example, some anime (yes Clannad After Story) have influenced me in the real life, and I will be more or less subjective on them.
I think this is more or less the same as a harsh grader scoring some humanity papers.