Advice on Revenue Build

Dipping my toes in the water in undergrad with creating Excel models. Feel confident using sales X volume, Top-down, bottom up revenue assumptions for expected revenues, but struggling to adjust COGS, SG&A, R&D, and interest expense to scale with revenues. Anyone have some helpful tips / best practices they use when it comes to this?

(I know there are hugely helpful in-depth modeling courses on here to answer this exact question, but I already shelled out for a financial modeling course through my undergrad that starts in a few months and I'm trying to go in w some context.)