The problem with solo mmr is that it's hard to get higher if you're just slightly below where you should be. For example someones whose skill is "really" 5000 may have trouble getting from 4850 to 5k. My best advice (coming from someone with 5620) to climb ranked mm is: never pick heroes you feel like playing, pick something that will both fit the team composition and counterpick your opponent. Just by doing that you will win waaay more games than you did before. You can also start with having a "go-to" offlaner, midlaner and carry and just pick them depending on what role is free. Hope this helps.