Let's start with the least formal and easiest way to get some CPD under your belt. Join Twitter or more specifically Edu-twitter as it is sometimes called. Create and account specifically for teaching and start following some of the most experience educators on the planet.
Here's some accounts I recommend to start following:
Clayton Stott @mrcstott (shameless fish for followers!)
These are the 'educelebs' on twitter, I have missed loads of people off but if you start on Twitter you will find your own way.
Jonny Hall @studymaths
Mark McCourt @EmathsUK
Bernie Westacott @berniewestacott
Robert J Smith @RJS2212
Ed Southall @Edsouthall
Jo Morgan @mathsjem
Tom Sherrington @teacherhead
I'll be honest at this point I'm not a big one for reading but I know some of you will be. Here is a list of books that I have either read or being recommended along the way. Most should be easy to find and purchase on Amazon.
'Yes But Why?' Ed Southall
'Making Every Maths Lesson Count' Emma McCrea
'How I wish I'd taught Maths' Craig Barton (has multiple books)
'Teaching for Mastery' Mark McCourt
'Thinking Mathematically' John Mason
*Not Maths* but anything on Cognitive Load Theory
I do like to listen to a good Maths/Education podcast often on my commute (20/30 minutes). Here is a selection you may find interesting:
As a non-specialist Maths teacher and being at a supportive school I have had the chance to experience a few CPD courses over the few years I have being teaching, here's a list of ones I have either attended or have been recommended to me.
If you don't already have an understanding I recommend developing knowledge on cognitive science. I believe most providers will cover this during teacher training nowadays but it really is important to have a grasp of the key areas.
I'm not going to recommend any reading here as I still don't feel confident enough myself and there is much better people out there to advise on this area. The people I would recommend following on Twitter or looking for their work would be:
Daniel Willingham
Adam Boxer
Tom Sherrington