How do you rate movies?

My advice... make proper use of the rating scale! ; it's really that simple.

that's not hard to do as movies you find to be average (basically watchable but forgettable) give them a 5/10 and then it scales up and down from there based on your overall enjoyment of a movie. this is definitely the best all around rating scale as it makes the most broad use of it.

but in a very basic sense for me movies are ultimately apart of one of two categories which are...

5/10 and less = Thumbs Down (won't re-watch(with rare exception))
6/10 and higher = Thumbs Up (will re-watch)

but you said you rate movies a 7 or 8 most of the time... most movies simply are no where near THAT good assuming you see a 5/10 as average (most movies (as in more than 50% of EVERYTHING i have seen) tend to land here) and then it goes up and down from there. plus, this assumes you have seen many movies as this helps you rate movies better this way as you know what's really great to above average to average and below average to crap etc.

here is my rating scale which is pretty similar to the vast majority around here as while they might word theirs a bit differently they mean pretty much the same thing...

10 = As much as i can enjoy a movie, pretty much.
9 = Nearly as much as i can enjoy a movie.
8 = Great.
7 = A Strong Thumbs Up. (My Favorite Movies score here and higher which currently contains 196 movies(i have seen over 2,100 movies))
6 = A Mild Thumbs Up. (My minimum score to re-watch a movie)
5 = Average/Forgettable/Thumbs Down. (while a negative score, they typically don't waste my time)
4 = Below Average.
3 = Failure. (i typically finished watching these movies, but they are just bad)
2 = Boring. (i could not finish watching due to boredom and boring is pretty much the worst crime a movie can commit)
1 = Greatly dislike. (a rare feat, in a negative way)

for measure... most movies i see get a 5/10 with a 6/10 being the next most common and between both of those ratings that makes up over 70% of everything i have seen.

to state the obvious... i ultimately rate movies based on how much i enjoy them. the further they get away from that, the lower the rating.

with that said... i noticed some consider a 7 or higher as positive and a 6 or lower as a negative, which is what i used years ago, but that's too limiting as way to many movies get bunched onto the 7/10 score that way even though some are clearly better than others which is where having a 6/10 rating as a positive comes into play as that's more of my 'mildly like' range of movies and makes the 7's and higher more valuable this way etc.

trust me... use a rating scale similar to myself, you won't regret it (anyone who's rating scale varies too far away from what i have is flawed(this is not some ego thing, it's simply looking at the rating scale mathematically with the center being average and then scaling up and down fairly evenly from there based on your overall enjoyment of a movie)).

another thing... only you can determine what to rate movies though but i feel once you have seen a lot of movies you can tell what's genuinely of higher interest for you and what's basically "just another movie" etc.

i am sure you get the gist of what i am saying and i have said more than enough for you to have a solid rating scale for yourself

p.s. the majority of movies i see get a 5/10. if i include 5/10's and 6/10's that makes up for basically a bit over 7 out of every 10 movies i have seen in the long term (i.e. 70%+).