I've been using this criteria for what I watch or drop since around 2010 or so.
New IPs (AKA original shows like Madoka Magica)
New Adaptations (any product that has not yet been produced in anime form)
Sequels that I gave at least a 7 (Baseline for good)
Sequels of shows that I might not have liked but have gotten so much attention that I feel compelled to watch (Sword Art Online)
Sequels because why not.
Drop: (Supersedes Watch)
Any show that fails the first episode treatment (very rare, this is where animation style or quality has the largest weight, it has the lowest overall weight when I think about my overall score).
A show that has a consistent string of episodes I'd give a 4 or below (normally 3). This is also kinda hard to do because often times an anime will have a pretty good episode in the middle of crap.
Any anime because "I'm done with this."
Locked: (Bypasses Drop)
Any time a show has over 50% completion is gets locked in to completion as long as it has 52 episodes or less in the final product.
The Ranking below is more for me to keep track of how much I like each show when I go to rate them at the end. I watch so much anime that at this point I need to judge it against other shows to really nail down where I want to place them.
Below is my weekly anime ranking. They take into account the entire season so far. Story driven shows are likely to suffer early in these.
Fall 2017 Anime Rankings (Week 1)
1. The Magician's Bride
2. Girls' Last Tour
3. Children of the Whales
4. Houseki no Kuni (TV)
5. Kino's Journey -the Beautiful World-
6. Netojuu no Susume
7. Food Wars S3
9. Blend S
10. UQ Holder!
11. Konohana Kitan
12. The iDOLM@STER SideM
13. Just Because!
14. Juuni Taisen
15. Black Clover (TV)
16. Two Car
18. A Sister's All You Need
20. Ousama Game
21. Sengoku Night Blood
22. Dynamic Chord
23. Tsukipro The Animation