Not just MVC. Study about MVC-2 Pattern. Then it will be easy for you to move to Struts, as Struts provides a clear implementation of MVC2. Also understand the difference between MVC1 Vs MVC2. Its very important for having a good knowledge on the basics.
Also a bit of custom tags would do, not much. Until and unless you gonna put your hands by developing some custom tags of your own, an exposure on the following would suffice.