How do you limit your skills in a video game?

If you're trying to keep it a secret (so no handicap modes or playing with one hand), there's really not that much you can do that isn't specific to each specific game.

Like if it were Smash Bros or something you could for instance avoid items or not use smash attacks or something. People tend not to notice that kind of stuff in the chaos of a fight.

But overall...All I can think of is to just subtly attack less and restrain yourself from dodging/blocking.

It depends on what you play. Like when I play Injustice with my girlfriend I play characters that I don't know how to play or are bad or I random. I also don't look up the move lists so I don't know what I'm doing. Sometimes I won't block for a game. Basically I let her win every few games so she will keep having fun without knowing I'm letting her win. If it's a shooter use a gun that gives you a distinct disadvantage.

Honestly I would just play like I would against anyone else. I don't know about you I wouldn't want my friend to go easy on me. I'd rather lose to you 100 times and win once while you were trying your hardest than have you go easy on me and let me win. Im sure your friends feel the same so dont worry about limiting your skills.