Reddit reviews How To Write Funny: Your Serious, Step-By-Step Blueprint For Creating Incredibly, Irresistibly, Successfully Hilarious Writing

I don't think you need to read the whole book (there's a small summary that's a few pages out there), but I found Greg Dean's book helpful for learning how to write simple setup/punchline jokes.

For improv (and it applies to sketch too imo), the UCB manual is the best book I've read.

For writing, this book from one of the founders of The Onion is really good. I think if I had to recommend just one comedy book, it would be this one.

https://www.amazon.com/dp/1499196121/ref=cm_sw_r_cp_apa_i_UH1GDbGMTW723

This book changed how I write jokes:
https://www.amazon.com/How-Write-Funny-Step-Step/dp/1499196121

It's all about subtext and joke forms. Very quick read.

https://www.amazon.com/How-Write-Funny-Step-Step/dp/1499196121

Wow thanks, I really need to hit a bunch of open mics and suffer some bombs to neutralize all of this validation.

I'm still trying to develop a solid writing habit to be honest, it's very difficult for me to maintain a steady productive flow.

I'd recommend reading Poking a Dead Frog by Mike Sacks and Sick in the Head by Judd Apatow, both are collections of interviews and advice with amazing comedians and comedy writers. You can get some fantastic advice there but mostly it's just inspiring and motivating.

For writing specifically, the only book I'd seriously recommend is How to Write Funny by Scott Dikkers, he was a founding editor of The Onion and it's a slim, no nonsense book.