architecture: can I improve the structure of my projects? If so, what sources can I use?

I know this is a completely general question, but I am interested in improving the structure of my projects, if this is not the right forum, I will go to the right one.

Now, about what I'm trying to improve, suppose I do an MVC or WEB API project in .NET
Normally the structure of my project will have the following structure (the DataLayer folder is just a test):

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And if I need it, I use a second project that is a common project, where I have my data layer, using an entity framework similar to ORM and many functions that I will use in other projects. The name Controllers is probably not the best because in this case they will be normal classes.

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In order to invest time making a better code, using design patterns, should I use subfolders to better organize my code? If the project is large, this becomes a disaster.
Are there good references out there that point me in the right direction?