How did you choose a main

Personally, when it comes to roles, I've been changing my main role every season just so I can learn more. I played Support mostly in S3, Mid and Adc in S4, Top and ADC in S5, and only started jungling in pre season 6. I intent on maining support in season 7 and keep it as my main role, as its the role I enjoy playing the most.

As for champs, I'm usually attracted to versatile kits. In S5, I played Gnar alot because of how much you could do with the kit. But I'm also a big lore lover, and the whole aspect of playing as a death made me an instant fan when they came out, and I always like to pull a game every now and then.

Overall, I think you should just play whatever you like. If your thing is to play all the OPs, then do it. If you want to main Teemo top, then do it. Doesn't really matter what you like, as long as you try to win you are still free to play it.

EDIT: Just noticed your name. I see you like .

i choose my main when i was level 1... i liked a champion, set my goal to buy it and i bought him and started maining him... for years.

I'd say first find a champ you find entertaining and that you feel like you want to master. If you pick a mage you can always try mid or top in some cases you can even play a mage as a support. In my case I thought that Thresh would be a good main for me because I like how he can change a game even if he is behind. I knew I liked support because I was not the best at csing and I was more focused on the map and objectives then my positioning in teamfights so I thought I would give the role a try.

Pantheon looked cool, like a Spartan, so i chose to play him a lot and that is who i gained for that reason lol.. That is literally it lol.