The biggest one I can think of is getting rid of arrogance.
Arrogance is a feeling of superiority that blinds people. An arrogant person will never look at themselves and realize that they're making mistakes. They'll never look beyond their position on things, and just insist they're right. Arrogance is the seal that Allah puts over the hearts of the disbelievers, and it works because they're too arrogant to notice.
It's also why we have "cultural Muslims". The kind who drink alcohol, or eat non-halal food, and try to justify it with flimsy excuses. I've had these people get outright angry at me for pointing out that they're doing wrong, and that anger comes from arrogance. These people believe that their alternative is better than the laws they were given. Either that or they believe that they're somehow special, and won't be punished. None of those arguments will hold up on the Day of Judgement.
Arrogance blocks our ability to worship Allah and submit to Him. If there's one thing you can do to try and better yourself, it's to be more humble. Realizing that you have flaws is the first step to fixing them, and arrogance will only get in the way.
Outside that, another thing that helps me is the reminder that no matter how badly you fuck up, if you turn towards Allah with sincerity he will forgive you. This doesn't mean that you can sin constantly and just ask for forgiveness when it's convenient, but it means that when you're ready to ditch the sins that are holding you back, you'll be given another chance. You'll never have to think "I've sinned this much already, I might as well keep doing it". In short, never give up on Islam.