plat 3 mid main here (maybe you can tell by my name), been plat for a couple years now maining mid with a variety of champions played
To me being successful as a mid laner in SoloQ is much like the real estate mantra that everyone uses "Location, Location, Location"
Being smart with knowing when to roam, when to stay in lane, when to recall, when to follow your lane opponent on a roam or stay and push their tower, you are the center of attention and everything around the map revolves around you. For instance if you roam bottom and force a bad play and die to an enemy adc, you've just put yourself AND your bot lane behind with a bad play. Your lane opponent gets free cs and mid control which leads to vision control, maybe they get a tower, etc etc.
The great thing about maining mid, and this is why I have mained mid lane as long as I can remember, you have so much variety when it comes to champions, whereas ADCs are usually stuck with only like 2-3 choices that are meta, the mid lane usually has a wider selection of strong champions.
Edit: A comment to an earlier post about awareness, I strongly disagree that "map awareness" is the difference between silver and diamond, that's simply not true. That's bad advice to give as it encourages you to not focus on mechanics or other very important skills as much as you should.