Probably the best overall resource I've stumbled on since I started writing has been Reedsy.  Reedsy.com is a marketplace for a variety of professional and other tools to help you on your writing journey.  I lucked out and found my Developmental Editor, Fiona, a partner who has helped me in my journey far beyond developmental editing.  

Aside from Reedsy - here is a list of my top 5 best writing resources so far...

1. MSWL.com
2. Publishers Marketplace
3. SCBWI
4. Querytracker.com
5. QTcritique.com

I rarely take advertisements for getting a book published seriously when I see them on Facebook.  HOWEVER, I am wholeheartedly endorsing the program called - "Get a Book Deal 101" AKA Path 2 Published. It's a 'Masterclass' taught by Kathy Ver Eecke.  Having been in the process for over two years, what Kathy teaches makes far more sense than any other approach shared with me.  Everyone needs to find the best overall resources for themselves, but having paid 3X as much for a similar 'coaching' when I first started my journey - I appreciate the approach and realness that Kathy brings to these sessions. They make a lot of sense to me and whether or not it helps me ultimately find the right fit in an agent - thinking differently using her advice has already helped me be a better writer.