How can I boost my Solo MMR in Dota 2?

Judge2020's answer is good, but one huge difference you'll notice if you see any pro games is how good they are at farming. Last-hitting is a HUGE part of the game. You'll often see 50-60 plus last hits for the carries/mid lane at the 10 minute mark and this makes a huge difference - 50 last hits gets you somewhere around 2-2.3k gold depending on how many siege creeps you get etc.

Practice your last-hitting, using the ingame last-hit practice if necessary. Get good at it and get the timings down for like 5-10 heroes and you'll see a big uptick in your effectiveness. If you're playing support this still applies but you should ideally be denying in lane to stop the enemy's farm.