Step one, stop feeling bad when you win. Or at least wait till the game is over.
Step two, find a few champs that you are comfortable and get good with them, whether they are strong at the moment or not. You will have more success with a champ you are comfortable with even if it is weak in the current meta. Then, see step one again.
Step three, when in doubt, don't. The biggest boost to gameplay for most bronze level players is just to focus on cutting down on stupid decisions. Reduce your death count. Don't worry about your game rank or carrying, play 20 games where you just focus on keeping your deaths as few as possible. If you aren't dying, you will have many more opportunities to make productive plays for your team and your stats will get better accordingly. In the end of the year recap for season 6, I saw that I averaged more kills and assists per game than Fakr, but I also had like double his deaths. The pros don't get 18 kills per game, they just make sure to stay alive so they are still there when the big moments come around. Play safe.
After that, practice and ward. And good luck.