While Superku and I do not agree on all things game design. Him being a green light game developer and me having never finished half a project. I would like to highlight the advice that he has given that has made the most impact on me.

1) Focus on mechanics
2) do not use shop sold assets - they never fit your art scheme and are hard the integrate
3) create a art style that is both simple and that you ( the game dev) can produce yourself - You do not know if you will gain or hold a art partnership and your project can be sunk if the artist leaves the team.
4) do not do a multiplayer projects - as first or second - or anytime you are not extremely experienced with multiplayer design and coding - in my case NEVER
5) be fluid and open to change, if something just doesn't work , drop it and focus on what does. Also be not tied down, if new ideas spark that fit - put them in.
6) Stay on one project and just keep going

Thanks Superku

lmao, even EA and Rockstar isn't experienced in multiplayer yet, still they produced tons of games with multiplayer features
Godmode in a multiplayer game (unlimited HP), teleport and more shit is the thing which follows.
Some day I hope to visit those companies and tell them that they have no fucking clue what they do..

Hm I'm doing some multiplayer stuff right now
But it's not really secure (C#).
Good enough for working out some authoritative server with reconciliation and lag compensation, and clients with prediction and interpolation.

Well I'm not a know-it-all but I think I'd (still) agree with all those points, and I think they are spot on as bullet points when I remember my old message(s) correctly.
I'm glad if my shabby advice can or could be of any help!

@Ch40zzC0d3r and @Firoball The advice about multiplayer was for me personally and after talks about my actual skill levels.

@All everything after the dash "-" is my elaboration on the Bullet-point of Superku's advice and should not be taken as a direct quote, more a mixture of the advice and my conclusions.

@Superku, yes I only meant to attribute the bullet points to you.
We do still disagree and design doc's and laying out full details. I would assume this is because you haven't worked as the unpaid-programmer at the whim of a designer or worked with a designer that is a 100% art person with little to no coding. the stories I could tell you about how if the designer would just fully express what he wanted in a doc, and how it would have saved me 20+ rewrites of every action, function or part of a function.... IT's maddening. The artist had me rewriting for days to make a bullet casing fall out of the gun in the proper way. Starting with no physics and ending in physics looking to non-cinematic. Designers that wish a player to act as if in a movie but write 3 lines of a doc... Maddening!
I understand your views from a solo developer, I hope you can see mine as a long time hired-gun(not implying pay lol).

Your Great Bro,
I might talk mostly on a path for newbies to learn, but once they do this is the advice they should focus on for a first game.