Ariana Grande, 1D and The Weeknd songwriter reveals his secrets

You're insecure, don't know what for…

You probably recognise those words as the first line of a very popular song. And you might even know the next bit.

But how do you write songs like 1D's What Makes You Beautiful - with their memorable lyrics good enough to be streamed over a billion times?

Chart-topping writer Savan Kotecha says his secret is "leaving no stone unturned".

"At least in the way I write, it's really just putting the time into the songs," he tells BBC Newsbeat.

Savan's songwriting credits include hits such as One Last Time by Ariana Grande, 2 Be Loved by Lizzo and The Weeknd's Can't Feel My Face.

You might think What Makes You Beautiful was about a One Direction crush - but you'd be wrong.

"I wrote that song about meeting my wife," says Savan. "So it's been a fun thing in our house that my kids know that it's about their mom."

Savan's big break happened when music mogul Simon Cowell gave him a shot at being part of The X Factor.

The TV singing competition launched the careers of 1D, Little Mix and acts such as Cher Lloyd.

"Once you start having hits, you start figuring it out - it took this [element] to make a song great and I'm going to apply a similar work ethic to the other songs."

Savan, from Texas, credits "a combination of hard work and luck" and "focusing on his craft" for getting as far as he has.

He adds it's important to not "just write it quick and leave it".

"It's making sure every part of the song is as good as myself and collaborators can make it."

The process varies from artist to artist, he says.

"Sometimes, somebody already has a sound and you're just trying to help them evolve that.

"Sometimes you're a best friend and therapist, helping them express what they want in a way that's digestible."

So what about his favourite collaborators? Savan thinks long and hard, before pointing to One Direction and Ariana Grande.

Ariana's One Last Time has been streamed over a billion times on Spotify, and Savan says he wrote it "after six months of bad writer's block".

"That was the first song that I played to Ari. So it started a really special relationship that I cherish."

He says the tune has taken on another meaning after the Manchester Arena terror attacks - being used "to comfort and heal".

During his time in the industry, Savan has seen change, with things "really exploding" thanks to TikTok.

"It's no longer record labels telling the audience 'this is your favourite thing'," he says.

"It's the audience saying: 'this is what we want to hear and are enjoying'."

But it can be "a much trickier time" for new artists and writers to break through because it's no longer just about being signed, warns Savan.

"You have to build your fan base, and you have to do all those things yourself."

So now he wants to help new talent to break through.

He's partnered with TikTok, Simon Cowell and other big names on a project called StemDrop.

It provides creators with individual components of a song such as drums, bass guitar, vocal parts - known as stems - to create and share their own unique versions.

Savan is part of a trio which has released 60 seconds of a new single on TikTok, with musicians able to access the stems from that song.

"It feels like the evolution of how the business can work, in which there are no more of these gatekeepers," he says.

"It also gives us a chance to collaborate with new writers that we normally wouldn't be able to."

And for those who find success and end up writing a good song, Savan says the hard work shouldn't stop.

"Challenge the song that you're writing, and make sure that it's as good as it can be," he says.

"Rather than just being happy you wrote a song, keep going.

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