Reading the the process gurus' books is good. Up to a point, but in the end what will really help you mature is years of developing software in a variety of environments and with many types of teams, projects and people. (This includes doing one-person development through organizations with thousands of developers and HUGE projects)
From those experiences (Assuming you are able to view the world around you) you can probably come up with your own ideas of personal, team and other processes and maturity levels.
The fact that you are interested in it and looking for answers about it is probably more important that subscribing to or reading a certain subset of authors or process books.
Read widely, practice software development and DO things. After all, this work is about producing something - don't lose sight of that. As seems to happen too often - some people fall down the "process" rabbit hole and are rarely productive after that - they pursue process as an end in itself. I should know - I drank the cool-aid early on but thankfully got a change of venue.
Anything you can do to rub elbows with developers from DIFFERENT kinds of teams or organizations is good - exposure to new practices and discussion of tools and practices is necessary to grow and learn. You won't grow as fast without exposure to new ideas. That does not mean you should jump on all the new, hot things that come along. Many times they should be rejected or left to mature, but in some cases, hop on and go for the ride.
Don't be afraid to try things and fail.
Process is often very dependent on the organization/team you are part of.
Process sure does have its place, but it is secondary - not primary - to producing quality products. Use your head and common sense.
EDIT
If you really really want names:
Gerald Weinberg has some decent books that are related to your questions. Tom Demarco and Ed Yourdon also are on the list.