Excellent blog post by James Edmonson (OHNO Type Co.) about vectoring letters, with invaluable tips for both lettering and type design.

Drawing Vectors for Type & Lettering | OH no Type Company

Can also recommend this series of posts by him about drawing letters in general; it’s filled with tips and important content but communicated visually and in a chill way.

Scott Biersack’s step-by-step tutorial of how he used to go about vectoring his letterings
https://design.tutsplus.com/tutorials/hand-lettering-how-to-vector-your-letterforms--cms-23248

Great tutorial by Glyphs about drawing with béziers showcasing good practices:

Drawing Good Paths | Glyphs

Article by type designer Fábio Martins going deeper into how bézier curves are made and how they behave:

Bézier Curves and Type Design: A Tutorial | Learn - Scannerlicker!

So What’s the Big Deal with Horizontal & Vertical Bezier Handles Anyway?

Dave Coleman’s blog post commenting the importance of keeping anchors in extrema and handles horizontal and vertical, showing examples of how other professionals vectored their letters and also how they used exceptions to that “rule”

So What's the Big Deal with Horizontal & Vertical Bezier Handles Anyway?

Adé Hogue

Bézi-yay! - Adé Hogue

https://web.archive.org/web/20211221173728/https://www.adehogue.com/journal/2019/10/23/beziermethod

Arrow Type’s Instagram post with a sped-up video of him building sans serif letters in Glyphs, showing how he uses parts of already drawn letters to build up other letters.

Illustrator

Illustrator's Pen Tool: The Comprehensive Guide

Vetorizani com Saiani

Series of mini-tutorials by Plau’s Rodrigo Saiani, with invaluable tips and tricks about Illustrator and letter vectoring (it’s narrated in Portuguese but you can probably grasp things by just watching the visuals).

BOOKS

Leslie Cabarga - Logo, Font & Lettering Bible

Logo Font & Lettering Bible

The book is a bit old, but has overall great content about drawing letterforms. Around page 130 there’s a specific part about letter vectoring tips in Illustrator.

COURSES

Phaedra Charles - Hand Lettering Styles and Techniques for Embellishment

Hand Lettering Styles and Techniques for Embellishment | Phaedra Charles | Skillshare

Marta Cerdà - Characters with Character

Online course - Characters with Character (Marta Cerdà Alimbau)