First I'd like to congratulate you for reaching out to the community for support. There are a lot of friendly and experienced players willing to help out.
Some of the first things you start to learn that make you a better player are positioning, last-hitting, and the often overlooked: communication.
Positioning: Where you stand, how you move, and when you do so all are very important to being successful in League. This will vary by role of course, but generally in lane you want to be close enough to get experience, far enough away to not be harassed, and angled away from the jungle as to be able to react to a gank. Teamfight positioning varies wildly by champion, role, and team composition, so practice is the best learning method for it.
Last-hitting: This comes with time. There's no real "trick" to it. It comes down to intimately learning your particular champion's damage, scaling, and animation speeds. Naturally, this will come with practice, so just keep it thoroughly in mind and work at it.
Communication: League of Legends is a team game. That means your success relies not only on how your teammates perform, but also on how well you interact with them. Pings are a great place to start. Learn each of the smart pings: when they are effective, what they convey, how your team reacts, and where to place them. Pings are effective because there is generally little bias attached. If you're having a bad game and your team is raging at you, your pings are still just anonymous enough for you to be helpful without causing a flame war.
Always be courteous to your team. If you're friendly and enthusiastic, you'll generally get a decent response and your team will be willing to work with you. This isn't always the case, but it generally helps, and at the very least will rub off on your mood and you may find yourself enjoying the game more. Toxic players are out there, and honestly your best bet is to not feed them fuel for their fire. If you ignore negative statements and keep everything you say positive, they won't have anything to keep them going, and your team can focus on winning.
That was quite the wall of text, but hopefully it helps. If you ever need someone to play with or show you some tips and tricks, feel free to add me.