Practice definitely helps.
There's a lot luck involved because there are so many candidates, most of whom cannot come up with an approach to solve a problem (let alone to solve it well enough to serve billions of users well). So even most candidates who are qualified can't convincingly demonstrate that given the time constraints and pressure etc.
It is hard to get into FANG for college new grads, it is even harder if you're trying to break into the tech industry from outside without the schedule flexibility and focused community support of a top tier university. It is possible but you need a combination of high ability, strong drive, and luck.
At my FANG, we've made some interviewing changes over the past 5 years such that these days you'd spend at least 20% of your day interviewing talking about what you worked on and achieved and how you solved problems, whereas in the past it would be entirely at your interviewer's discretion and typically only be a few minutes of unscored small talk.
FANG is an interesting life experience and it pays well, but plenty of people find it is not all it is cracked up to be. Just as in every job, a lot depends on the particular people you work with and whether you enjoy the particular problems you are solving. So maybe also consider whether you really need to go FANG (right now) or whether you could be just as happy at a place that's willing to take a more individual approach on hiring. That place could even be a stepping stone to reach FANG later on if that's what you want to do later.