League of Legends can be a behemoth of a game to wrap your head around in terms of all the information there is to digest.
Hopefully these few tips will get you through your first few hundred matches against bots and other amateur players, so that even if you aren't playing like an experienced player quite yet, you're thinking like one!
1. Stay in Lane, But Help With Objectives
This one might be obvious, but you'd be surprised how often players still do this at a higher level! The idea is that whilst you're in your lane, you're at your safest due to your tower being in range to protect you (unlike the Jungle), and you're getting more EXP and gold than you would elsewhere.
As soon as you leave your lane and start "roaming" the map, you aren't building up EXP or gold and you're starting to fall behind immediately. Unless it's to help out a teammate or to win a group fight and secure an objective, don't leave your lane, especially before mid-game. If a more experienced player tells you to leave though for a specific reason, you should listen!
2. Remember Your Free Ward
Everyone gets a free ward at the start. No, this doesn't mean you select a regular ward and your first is free - there are a specific set of wards that cost nothing, and you can swap between them as much as you like!
Whilst this is ingrained as muscle memory for experienced players, as a beginner you'll forget often about the free wards as you decide how to build your champion. Don't forget!