Harvard University's CS50 Games course has a free online version on edX. It's a great class for beginners with some coding experience, and uses Love2D and Lua. Nearly all of the concepts apply to PICO-8 development.

https://courses.edx.org/courses/course-v1:HarvardX+CS50G+Games/course/

It's not too difficult to translate in-class code to PICO-8 equivalent code, but it might be easier to stick with Love2D for the course, then figure out PICO-8 equivalents later. In-class code uses Lua standard library features, all with PICO-8 equivalents. Spreading code across multiple files could be done with code tabs or "#include" instead of "require". They also use a simple third-party object-oriented class package to teach OO concepts. This could be ported to PICO-8 but hasn't been yet.

If there's interest, I'm sure we could pull together a set of support materials for bridging CS50 and PICO-8. For now I'm just recommending the course.