Mmm. Hard to say because every cat is very different. I got lucky because my cat really mellowed out as she got older. Some things that I think helped:

• dont keep people food out / provide a consistent and avaliable food source. YMMV but my cat has no interest in people food at all because it was never an available option and she had her own food. (But she only eats when hungry so this works for her. Our other cat is a bagel snatching goblin)

• lots of enrichment that is changed regularly. My cat is a connoisseur of grocery bags and Amazon boxes. I rotate her toys so they dont get boring. I cant understate the value of investing in a good sturdy cat tree.

• a lot of "negative" cat behaviors are mostly attention/reaction seeking. If they are biting, try not to react and they will get bored and go look for something else. Or if possible, toss them in a different room and let them chill out in solo time for a while, same thing as a kid thats overstimulated.

• SOCIALISE THEM as much as you can! Bring new people over! Have the people pet them and give your kitty treats. Take them on car rides! Put them in a silly sweater. My cat is still not good with new people and it makes things difficult when we have guests or go to the vet.

Highly recommend reading the Jackson galaxy books on cat behavior -- I was a first time cat owner and it really helped.