New here, curious about scaling into positions on $SPX

Hey everyone, just joined. Been trading for about a year now, mostly dabbling with futures on $ES_F and some equities, but really trying to refine my process. One area I'm still feeling out is scaling into positions, especially on higher timeframes for trend trades. I often find myself taking a starter, and then when it moves in my favor, I'm hesitant to add more for fear of turning a good trade into an average one if it reverses, even with a clear invalidation level. How do you all typically manage scaling in, particularly when you're looking for sustained moves?