I generally only play by myself in ranked...I have only queued with someone once.
The way to climb is learning from your mistakes and working on mechanics and improving that way. I record my games and will rewatch them. Focus on 2 lanes, and only 2-3 champions per lane max. That way you get super familiar with those champs and can focus on the mechanics. Go for objectives over kills, roam if you have the ability to help out laners.
Premades can make it harder, but I've seen so many premades fail because they end up just picking one lane to bully and the others go unattended. Use that to your advantage