Also. Keep Ping-ing your team. Most of the time, this is the best way to get them to play the game your way and you'll be surprised at how well most of your team mates respond. My win rate drops MASSIVELY and then I notice that I have not been Ping-ing for a while.
Pings are ESPECIALLY important for ordering a retreat and preventing the enemy from striking back and Acing you because people aren't paying attention to respawn timers. Part of the reason games last so long and the team that has a lead doesn't always win is because of the needless throws on both sides due to these over-stays. ONE SINGLE PING to prevent a single over-stay could win the whole game because it lets you maintain that kill lead.
Pings win wars. Imagine you are a Red Alert 2 commander. You're just traveling in the battlefield in a tank (your champion) and that's your command post.
It should always be
Towers > Kills > Dragons
Once one side takes a few towers down and keeps the minion waves in your favour while grouping as necessary, its very hard for the other team to come back. Its much easier to come back if you're behind on dragons. I'd rather have several towers down then a dragon.
Also, stay the hell away from Elder Dragon. Its a noob trap (you don't need it if you're ahead... it risks a throw... if you're behind, its not worth the risk). I've noticed that more often than not the team that tries to take Elder first (ahead or not), loses.
...
The other thing I notice is that without pings, people often have bad combat formations late game where they have something like a 3:1:1 (2 way single split). This is prone to throws because you will have portions of your army run into larger bits of the enemy's.
Late game, except for situational and temporary splits to clear waves and make picks... it should ALWAYS be either 5 or 4:1 (with the 1 split pusher). I'd recommend sticking to 5 because the 4:1 plays require A LOT of communication, military discipline, and strategic awareness.