If your question is: how to get good at regex...

Remember that regex is a separate language and you have to learn this language. You don't have to learn all of it at once. You can learn a bit at a time but to get good you must keep studying.

You can read the manual pages: perlretut and perlre are good places to start.

There are some tutorials here: Pattern Matching, Regular Expressions, and Parsing.

O'Reily has Mastering Regular Expressions.

Most of all, you must practice. There are lots of questions and answers here that you can study. Try searching for 'regex' or 'regular expression' in Super Search. Try writing your own solutions to the problems you find. In the beginning, some of the problems will be too difficult for you, but if you keep reading and keep practicing, you too can be good at it.