New here, curious about scaling positions after initial entry

Hey everyone, just joined. I've been paper trading for about a year and starting to feel more confident, but one thing still trips me up: how do you guys approach scaling into a position after your initial entry? Say I take a starter on $SPX, and it moves favorably – do you have a specific percentage of profit required before adding, or a fixed amount of additional capital you're willing to commit, or is it more about market structure confirming your bias further? I've seen different approaches and I'm not sure what balances risk with potential reward effectively. Any insights would be great.