If you are starting to get bored of League of Legends

Try spicing things up. I think that a lot of people are constantly playing ranked, spamming the same champions over and over and at some point feel frustrated because they can't improve as quickly anymore. It starts getting pretty stale once you've reached the cap of easy improvements.

If this is the case, try this: Get mastery level 1 (or 2) on EVERY champion in the game. Do this in normals, not ranked. You'll be surprised how much fun you can have when all the pressure to perform falls off from your shoulders. When you are playing a new champion, you have nothing to prove. You are just testing them out. If you go 0/8, so be it. Your goal at this point will not be to win, but to at least get a good moment in the game. Try to sneak off a kill under your own turret or something. If you're doing this challenge, you'll be surprise how rare these moments are. I have done it a while ago when champion mastery was released and I'm starting to do it again (towards lvl 2 this time) and I must say I haven't had so many S games in a row for a long while. My primary focus is to not feed. And when you do this, you'll suddenly see yourself having multiple kills and assists out of nowhere (of course not every game). Just played a game with evelynn jungle where I got executed by red buff in my first run (I did gromp -> blue -> red) but then I went botlane and assisted ezreal in a triple kill. After that I went bot a few more times and their inner turret fell shortly with a ton of kills in our pockets. It was hilarious to be stomping so hard with a champ that I hadn't played in a while (and maybe played like 5 games with EVER), even though I still sucked with the champ.

TLDR when you're bored, stop playing your main champions. Try out something fresh, experience with every champion in the game even those that you think you'll never like. You can get pleasantly surprised.