Sitecore 9.3 Visual Studio setup help - errors on deploy

Make sure you have set the dlls in visual studio as "copy local to false" in their properties to avoid errors as given in the following official Sitecore documentation :

https://doc.sitecore.com/developers/93/sitecore-experience-manager/en/set-up-sitecore-and-visual-studio-for-development.html

Also, make sure your controller is having a parameterless constructor like below

public MyController()
{
   //stuff
}

EDIT : (Tip) If incase your site crashes - you dont have any solution/fixes and you don't have backup, you can still find the entire folders and files of a vanilla Sitecore instance inside the installation zip file (Sitecore 9.3.0 rev. 003498 (OnPrem)_single.scwdp.zip/Content/Website). You need not install a new Sitecore instance again.. :)

Specifically, set the copy local to false for System.Web.Mvc.dll besides the regular dlls such as Sitecore.Kernel, Sitecore.Mvc, Sitecore.Mvc.Analytics

Basically, if it is a dll version mismatch after deploy/publish to your webroot folder, then you would get error message such as

Could not load file or assembly 'System.Web.Mvc'...