What is the most efficent way to make a transitional serif?

I’d try using guides and the Align panel instead of drawing each serif manually with the Arc tool. Creating one clean serif shape and reusing or duplicating it can also help keep the proportions consistent across letters like “A”.

If you mean designing a transitional serif typeface in Adobe Illustrator, the easiest approach is to start with a classic serif reference, build consistent letter proportions, and use the Pen/Shape tools to create clean bracketed serifs. Keep the stroke contrast moderate and refine the curves with the Direct Selection tool.