To get on steam you need to get greenlit (via user votes, so you would need to get alot of hype around your game) or get valve to notice you. Again you'll need alot of hype. If you want to use PC as a platform, i would suggest distribution via a personal website plus the suggestions above.
Mobile, you just need to purchase the developer packge via apple (100$) and you can drop your game on the app store. I believe android doesnt require a dev package....i could be wrong about that though.
My suggestion is get your game out there on as many platforms as you can right now, and hopefully get your name out there. Then, with some luck get noticed by Sony/Valve/Microsoft and get your game on their distribution platform, and really start bringing in the $.