More often than not I just go simple pencil all the way through.
Sometimes I use a Pilot Coleto Hi-tec C multipen with four different colors to make things more interesting and differentiate between types of data, particularly within the boxes so I know what happens from one box to the next, particularly when going back to prior boxes to add in historical information. (I also tend to go with their 0.3mm fine tip ink refills for being able to pack more writing into small boxes!) Sometimes I'll do the starting pitcher and their work in black, and relievers in blue, purple, and orange rotating through to differentiate each pitcher's work to make it easier to keep up with their individual data, especially when I do full pitch counts.
Sometimes I'll take along a Mitsubishi 772 "editor's pencil" that has both red and blue lead to add in some color. Often it's a simple line for pitcher changes or for substitutions across an individual line to distinguish when a sub came into the game.
Sometimes I'll use a typewriter with a bichrome ribbon and switch between black and red ink to help break up some data, or to highlight things like RBIs to make summing things easier in the end. Example: https://www.reddit.com/r/BaseballScorecards/comments/1s33f1d/20260324_tampa_bay_rays_vs_atlanta_braves_spring/ which has red lines between pitchers and red "I"s to break up substitutions.
Looking at example cards that get posted here will give you some ideas and pointers. Usually one can puzzle out what the scorer was doing using different colors or highlighters.
A lot of how I score depends on my mood, where I'm watching a game, how much time I want to put into it all, and which tools I have at hand. Experiment. Have fun. Do what works best for you. There's no single "right" way, just the same way there are thousands of different formats in scorecard formats.
reply to u/Alej_Betancourt at https://reddit.com/r/BaseballScorecards/comments/1s3mbzt/your_advice_for_a_rookie_highlighters_and/