Solo Queue is difficult because you're playing a team game where you have to rely on others to win. You are forced to put your faith in people who can easily be incredibly bad at the game or who may flat out refuse to communicate or pay attention.
Sure people will always say "What can you have done better?", but that only works up to a point. Sooner or later you're going to need to find a viable way of ensuring your team's victory outside of they hypothetical.
Here are some things you can do to increase your chances of winning games:
1. Aim to carry
You know your capabilities better than anyone else on the team in Solo-Queue. Play to your strengths. Pick your good champions. Dominate the game.
2. Don't pick a champion simply because it's a 'counter'
This is big. Just because, on paper, your pick is a counter to the enemy laner, doesn't mean you're going to automatically do well and win. You probably don't have nearly as much practice with that champion and as such, are more likely to lose your lane and by extension the game.
3. Play an influential role.
This is also important. Each lane/role has influence, duh. But some have more game influence than others. How far along in the game this influence becomes apparent tends to vary from champion to champion.
Junglers are one of the most influential all throughout the laning phase and quite far into the mid and late game for their objective control and their ability to deter enemy laners. Many junglers also scale well into the late game and become a splitpushing god. I recommend players choose jungle if they want to have a feeling of control over the game's outcome.
4. Choose a few champions you like for that role and stick with them
Knowing a few champions by hard and absolutely pubstomping with them is far better than barely knowing a lot of champions and doing okay/bad with them.