How to win/not throw games
If you are here for any type of help, you most likely need this advice.
Know where your teammates are, know where your enemies are. Unless you and your team mates are unthinkabley fed you should never enter an uneven team fight. Just because your enemies are 5 man pushing mid does not mean you have to all in. Hold tower until they diffuse, or your fifth makes it to the fight, and punish missteps. This can also be a great time to split push while you can see all enemies in one area. Objectives win games.
Don't chase when you cannot see any other enemies on the map. As fast as you are gaining on that potential kill, their allies are gaining faster.
Don't go in for objectives or team fights when your lanes are pushed. Pay attention to the dragon timer and push the lane out around 1min till dragon. If the enemies lanes are pushed and dragon ends in a team fight that your team wins you can most likely pick up a turret. Generally team fights should only be for contesting objectives.
And always remember it's dangerous out there, take one of these 