Rule #1 You are bad. Everything you do can be done better by someone else. No matter how much you play, no matter how good you get, you will always make mistakes. And that's okay. You're gonna have games where you get stomped by player playing champs that feel unfair either because they are played by more skilled players, but just as frequently because you don't understand how they work. Mechanical skill and knowledge are two separate and equally important things. And you don't have to be good to have knowledge. In fact you learn more from losing than from winning. The important thing to takeaway from this is that even the worst player can know more about the game than you and you should be willing to take criticism as long as it is productive criticism. If they are rude and raging then mute and report them. But if they are simply frustrated then try to make a plan to win the game with them.
Rule#2 Communication is everything. Using it to coordinate as a team will allow you to beat more experienced players on a regular basis. Master the Smart ping system, it's your best friend.
Rule#3 Learn how to lasthit. During the laning phase your focus should not be kills. It's lasthitting minions. Basically, don't attack minions until right before they are about to die. This keeps you from pushing to tower which makes you less vulnerable to being ganked by the jungler. Additionally your opponents are going to frequently try to push their lane. This means they will level up faster, but that you will be farming under your turret a lot which is easy to do once you know how. It also makes them vulnerable to being ganked by YOUR jungler. There are advanced mechanics regarding this, but they don't matter if you don't know how the basics work.
Rule#4 Bot games are good in moderation, but playing them extensively will make you a worse player. Bots have predictable patterns that players don't and learning these will only make you more predictable to play against.
Rule#5 Don't watch highlight reels.