The way I see it, there are 3 primary reasons to ban what you ban.
There are some minor exceptions (such as newly released/reworked champions), but those are the major 3 points. Which ones do you most commonly ban and why?
It's whatever counters me personally, not necessarily my champion.
Most of my bans are on champions I can't reasonably fight, or even escape in a 1v1 scenario. Wukong, up until this patch (which thank god he's been nerfed) held that spot for a long time. The others are just ones I don't want to deal with fighting, regardless of whether or not they're strong. Fiddle and Heimer are usually these fallback bans, simply because nobody wants to deal with a lane Fiddle, or against Heimer anywhere.
If even my fallbacks are already banned, though, most often I'll just ban what I expect my team to not be able to handle.
Often i'll ban a counterpick of our first pick. If i have a high pick i'll use the ban to counterpick my own lane, but if i'm picking late, i figure i'll be the one counterpicking.
i either ban a counter pick to my lane or a champ that i know the team at my elo has issues with. if i know my teams win condition is mid/bot/jungle ill ban a champ that lets them carry easier. i typically play a tank top lane so. i need my other lanes to win and carry
Mixed between 2 and 4, I always insta-ban 
if it's a rotative mode or if I get to play ranked with friends, don't want one in my team (the feeder one) or one in the enemy team (the 12 years old bragging about his skills getting fed by the trash 
mid)
If I get Top/mid/jungle, I ban to protect my top laners matchup. If I get bot lane, I ban to save my support from getting counter picked.
Shit that my team will feed
Requires an attentive team that works together
Disables or disengages any and all ranged champions with windwall or projectile abilities
Literally removes himself from the game
