Begin by studying the magnetic effect of electric currentand magnetic materials. Then, look at magnetic circuits. Everything should be crystal transparent. You can then study each machine one at a time beginning with DC machines and transformers. Know how electromechanical energy is converted process in rotating machines. Learn about the power transfer within transformers and AC circuits should be crystal clear.
Induction machines are the next option and as well as synchronous machines.
Knowing about magnetic circuits is an essential part of understanding any electrical device Therefore, ensure that you are able to study it thoroughly.
There are NPTEL seminars on machines that are the most beneficial. Most important of all is the power of your imagination.