Here is a collection of links as well as helpful guides and tutorials other game developers shared. Please understand that the entries in this playlist will always be all over the place, due to the many gaming genres.

Please be aware that I might include tutorials for games that are typically aimed at adults. Those developers work just as hard as others and I do not see any reason to discriminate. Regardless, those entries can be hidden by filtering "A"-rated content.

And the last entry is for inspirational and motivational purposes.

Please Note: This playlist will look a little empty in the beginning. Give it time... (If you encounter good tutorials for game devs on NG, please consider sending me a link. My inbox still has some free capacity left. ;) )

Various Helpful Links:

First off: This playlist is an extension to the Guides, Tutorials & Other Help playlist. Refer to the latter for advice on self-publishing, Newgrounds, drawn art, animation, and a lot of other topics.

How do I make my stuff better/better stuff?

How to improve the quality of your (flash) game (by Yatsufusa) (Warning: Safe site, but not hosted on NG!)

ActionScript 2 Main: Tutorials and Resources (by JackSmack)

Are you still using Unity but can't decide what game engine to switch to? (by Markanime)

How to Submit Scratch Games to Newgrounds (by RaIix)

Assets

Free Art and Game assets. (by MindChamber)

You can find free bits of free-to-use audio on itch.io as well! (like this one) You can also find some free moans over there, in case you are making an NSFW-game. ;)

Newgrounds Medals

What are "Medals"?

Medal Guidelines

Adding Medals to your Game

Newgrounds.io Support in TurboWarp (Chapter 3 also deals with medals) (by ElRandomGMD)

Special Mention: Broken Medals

Far too many aspiring game developers release their games in a broken state - often enough, the medals will also be broken. Your game will do fine with or without medals. But if you promise medals, and you waste players' time, you should be prepared for medal collectors to rate your game considerably lower than if it did not make empty promises in the first place.

Just so you know: No matter what excuses you make, if I notice a game with "currently" broken medals, that game gets listed. And if there is no warning in the description, that game also gets zero stars from me. And the chance that others will do so as well is "not zero"...