There are several essential life and death patterns that quite commonly occur in games, however can be quite tricky to master. I think knowledge and familiarity with many of them are vital (necessary but not sufficient) for becoming stronger (reaching shodan and beyond).
If you’ve never heard of patterns like L groups, L+1, L+2, J groups, J+1, tripod, notcher, long L, door group, hovercraft, carpenter’s square, etc, and you are a DDK working toward SDK, or even an SDK working toward dan, then I think the below linked resources are valuable.
You could also figure out a lot of these patterns on your own by solving enough tsumego, but I think at least for some, systematic study could be beneficial. There are definitely many other great resources, but here are a few that I know about and found to be helpful.
1. Sensei’s Library
Sensei’s Library has a great catalog of common life and death shapes:
In particular, see the “Corner Shapes” and “Side Shapes” sections.
2. “Life and Death” book by James Davies
James Davies wrote a nice book called simply “Life and Death”. Each chapter focuses on a pattern or concept, spends a couple of pages discussing it, and then provides about six problems to further explain and explore variations.