I've worked with regular expressions for a long time now, and I'm always working on getting better at them. I ran across this 20-minute YouTube video and was really blown away by how quickly it explains everything you need to know about regular expressions. I highly recommend it.
Many of his other videos are also worth your time.
One huge caveat aimed at those in the world of Enterprise Software:
Not all products support all features of the regular expressions described in the video, and there are often nuances to the exact functions that are supported. For example, the following features described in the video aren't supported by various versions of *some* components of Netcool and ServiceNow, depending on which regex engine they use:
- look-ahead and look-behind operations
- named groups
Because of cases like this, I always recommend that you try to accomplish your goal using the simplest regular expression features as possible, and always test your regular expressions. Regexr.com is the site used in the video, and it is very powerful, but it appears to support the latest and greatest JavaScript regular expressions, with no way to change that. Regex101.com is the site I normally use, and it allows you to select one of several "flavors" of regular expressions.