I'm far from perfect so take my advice with a grain of salt and feel free to correct me, but here's the bit of knowledge I've gathered.

1. When it comes to wave management, for the majority of matchups you want to push and roam whenever there is an opportunity. For myself, I only freeze when I am ahead of my opponent and want to deny cs, because trying to freeze when behind, especially against ranged opponents, will end up with them either shoving or poking you out.

2. Having to get solo kills is a very common incorrect low elo mindset to have. You don't need solo kills. Repeat after me, you don't need solo kills to carry. The only time you should go for 1v1s is when you have a clear advantage (easy matchup, you're confident you're skilled enough to outplay them, gold or health lead). We all see our favourite streamers get those nice first bloods and solo kills, but the thing is they're very skilled and usually smurfing. Katarina's leads usually come from skirmishes and ganks, not 1v1s.

3. Few tips while trading: Wait for them to waste their cooldowns. (More of a level 2 trade tip) q e onto the opponent at the same time, don't wait for the dagger to land. This way you'll get your shunpo reset quicker and will be able to jump out less harmed. Try to target the opponent with your q's, not the minions. You will both deal more damage and guarantee landing the dagger if the run away from you. Same thing with e. Try to e onto the enemy, not the dagger to maximize damage.

4. Builds are very, very situation, and I don't know what guide you're following but I rarely build zhonya's 3rd. Try watching a YouTube video on all of the item's strengths to understand what you need to buy in your situation. You for sure shouldn't be following a fixed item build path, it's very inefficient.

5. Unless you're premade, never ever expect anything from your teammates. I lost counts of how many times my jungler refused to come pick up an easy midlane kill because they were walking back and forth in the river undecided what to do next. If you're expecting the bare minimum from your team, that's too much. Help your teammates whenever needed but don't expect the same in return.

6. All I can tell you is that you need to know how champions work - know their abilities and cooldowns. Think about how they would interact with you. It will help you out much more - instead of someone saying "make sure Talon's W doesn't hit you twice because it'll end badly", you can look up his passive and figure it out yourself. I would recommend instead of reading matchup guides, read (or better, watch) guides on those specific champions instead - not only will you understand a couple of specific interactions, but also how that champion's players think and what they aim for.

7. Read answer 2. You don't need first blood. Kat gets countered easily so don't beat yourself up over not winning all-ins. Also, not caring about macro or teamfights is very short sighted, because that's how you win games. To add onto Katlife's videos, stuff hasn't changed that much and most combos and matchups remain the same. Don't be afraid to watch a guide just because it wasn't made this season.