- How to manage waves so that side lanes are pushing
Well typically you have someone go to push the wave in, but you can set up a slow push by simply killing off the range minions in a minion wave, eventually it'll build up a gigantic wave to work with if left alone.
- How to siege effectively/ defend effectively
The unfortunate thing is that in some cases, there are teams that literally can't siege or defend against a siege, or even situations where your team is outmatched in siege power. When honestly the best type of siege comp is one with good wave clear as well as strong poke, it's the same for defending against sieges. Back before the mage rework I was an avid Xerath player, and I ran the old Athene's all the time because I could siege pretty much forever, endlessly wave clearing, and poking at the same time. The issue with siege comps is that you don't really want them for standard dynamic queue unless you're in a premade as they require coordination or a primary siege champion to be played exceptionally well.
- How to not throw at objectives
Take them, safely. For Baron, kill the entire enemy team so there's zero risk on a steal, same for Elder Dragon. Don't over commit for turrets, usually getting a kill or two allows for an easy take. If you're on nexus turrets and the enemy team has death timers below 10 seconds, walk away. The over excitement to end the game is where I've seen the most throws.
- What is the best way to end when ahead
Grouping up when ahead is usually the best strategy unless your composition sucks at team fighting. You basically need to identify the win conditions for your team. Do you have a split pusher, do a 1-4 split. Team fight comps should engage a team fight, most people try to siege with them and that's not how they work. Siege comps are self explainatory, you get some weird blends and such as well, but it's about figuring out what your team is better at, and how to win using that.