The singer, who won the 2009 series of the ITV1 show, reflected on his experience working alongside Syco boss Simon Cowell. In his letter, published in the Daily Mail, McElderry warned Little Mix and runner-up Marcus Collins that they should give the music mogul their true opinions.
"You'll find it isn't really about coming first or second. I don't believe, Marcus, that you will have more creative control than Little Mix because you came second," he wrote. "It's up to you all to take it to the next level. There's no rule book for popstars. Everyone does it differently. X Factor is an amazing platform.
"You are in control of your own destiny. I know people think Simon Cowell is in control, and yes, sometimes you have to follow what the record company says, but Simon likes people who can stand up to him, who say: 'I don't want to do this', or, 'I like that song'."
On Cowell, McElderry continued: "He's a very busy man and spends a lot of time in America, so most of the time we'd chat on the phone, but now and again I'd go into the office and he'd be there and we'd chat about songs. I'd say: 'I'm not keen on this one and I really like that'.
"He'd say: 'Can you try this?' It's about building a working relationship, not who controls who."
He went on to advise both to work with their respective mentors Tulisa Contostavlos and Gary Barlow on a "professional level".
"Like any job, there are going to be disagreements. If you don't like certain outfits, or aren't happy with how you are asked to perform or even what you are asked to sing, then have a discussion about it. Talk about it honestly or you're not going to do your best," he advised.
"You've got to be comfortable with everything you do because you're the one who has to sell the product. If you are not comfortable and it means having a bit of a row so long as it's constructive and not a tantrum I think it's fair enough. It's important to remember you are the artist, you have to keep creative control. Trust your own decisions."
The singer left Syco after the release of his debut album Wide Awake, but wrote that he "never felt down about leaving", adding: "I was thankful for the opportunity."
"When I look back I don't think I did anything wrong. I was always myself throughout the whole X Factor experience," he said. "The only thing I would have done differently is trusting my own creative decisions more and I would have thrown myself into it a bit more. I would have been more gutsy instead of worrying what people would think.
"Little Mix and Marcus: Don't be arrogant, you don't want to be divas, but grab everything. Just totally go for it."
> Joe McElderry previews 'O Come All Ye Faithful' music video - watch
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