how to put cards in sleeves without damaging them in the process?

ok so basically i pulled a fancy card at the prerelease and i just sold it to the lgs. they graded it as lightly played and gave me slightly less money for it, citing that it had some scratches. i have a feeling that i might have nicked the card while putting it into a single dragon shield.

is there a proper way to be putting my cards in a single sleeve while preventing the top of the sleeve scraping the bottom of the card? i feel like this must be a skill issue lol and i wanna fix that before i damage more of my cards

i know i should be double sleeving all my cards, but does that offer any protection in this situation? wouldn't the bottom of the card still be vulnerable while putting it into the outer sleeve?