I form my initial thoughts after a complete ride on the coaster. Usually I have a general idea of where I will put the coaster in my rankings when I'm sitting on the brake run. As mentioned on the home page of this site, I'm aware that I have some unique preferences and opinions for a hard-core coaster enthusiast. When it comes to airtime and intensity, I'm more like Goldilocks rather than "the more the better." I like a balance of grace and forces. While the sensation of negative G's is neat, if airtime on a roller coaster is uncomfortable, too abrupt, or leaves thigh bruises (parts of Magnum XL-200, Steel Vengeance, Mystic Timbers, Steel Eel, and Boardwalk Bullet to name a few examples), then I'm not crazy about it. I value speed, inversions, floater airtime, pacing, and smoothness/restraint system most when I rank roller coasters. I also love launches! Things like scenery, statistics, reliability, operations, duration and originality usually do not impact my opinions greatly.
I make a decision within 24 hours of my most recent ride. I'm not a person who changes my mind after months of pondering over where to put a coaster in my rankings. I also don't move coasters because other enthusiasts agree that a certain ride has gotten better or worse. For example, a lot of people consider Scream! at Six Flags Magic Mountain to be one of the worst B&M floorless coasters due to roughness. The one ride I got in 2011 was not rough at all, so it still sits in my top 50 because I loved it and I will not say it's bad unless I re-ride and come to that conclusion for myself.
If I've ridden a coaster multiple times, then I usually rank based on how I like the coaster on average. In most cases, riding in a different seat does not substantially impact my rank for a coaster. The big exception is Raging Bull, which is so much better in the back row! On the other hand, Millennium Force is currently my second favorite coaster whether I ride it in the rain or shine, and front, middle, or back seat. My preference for Millie is the front left seat in good weather though.
I will group clones and relocated roller coasters together for ranking purposes (but count them as separate credits) so long as the ride experience is more or less the same. So, B&M Batman clones, wild mouse clones, kiddie coasters, Vekoma Boomerangs, and Titan/Goliath each hold one spot on my list. I do this because I make the rules ;-) and I don't want to affect coasters in spots near clones by overstating or understating how much I like them. However, there is one cloned model, the Vekoma SLC, that I do NOT think is created equal across the board. T2 is one of the worst coasters I've ridden, while I think Flight Deck and Ednor L'Attaque are just OK, and Thunderhawk at Michigan's Adventure even made my top 50 until 2021. Therefore, those 4 coasters have separate spots in my rankings.