There are several ways you can improve your lua scripting knowledge, both from direct roblox websites and from youtube tutorials.
In terms of roblox websites, the API reference as well as just browsing the dev forum are two great ways to improve your lua knowledge without leaving roblox. For youtube, several channels such as AlvinBlox and DutchDeveloper are great sources of lua information, though its mostly a case of looking for what you need in the moment.
Alternatively, a majority of developers including myself have learned from reading, dissecting, and modifying game codes that have been open sourced by their developers. If you are interested in learning this way, I personally recommend Ruddev’s Battle Royale and Miner’s Haven as they are examples of what great coding looks like.
Overall, scripting is typically something you have to learn through trial and error, so if you take enough time just making a game, even if it’s not the best, you’re still going to learn more and more each time. It’s a matter of putting in the effort over long periods of time to perfect each individual skill.