The 26-year-old is desperate to claim at least a medal - something she has yet to do at a major global outdoor event.
The heptathlon gets underway on Wednesday and Johnson-Thompson does not want to suffer a similar fate to her disappointments at Beijing 2015, Rio 2016 and London 2017.
"I have to be at my best if I want to win," Johnson-Thompson told the BBC.
"I hope so [that mistakes are over]. Obviously, you never know with the heptathlon - there are so many different opportunities to have those slip-ups.
Silver medalist Katarina Johnson-Thompson of Great Britain congratulates Nafissatou Thiam of Belgium on winning Gold in the Women's Heptathlon during day four of the 24th European Athletics Championships at Olympiastadion
Image credit: Getty Images
"You do get bad performances and good performances," she added.
Unfortunately, with the level the event is at at the minute, a slip will cost you medals - even if it is just a small one - because you have to be at your best.
"I am just trying to make sure I am consistent every time I step on to the track and that my preparation and also my training is consistent.
"All I can really do is be consistent across the event and hope for a big performance here and there and see what happens."
Johnson-Thompson triumphed at the World Indoor Championships and added Commonwealth Games gold and European Championships silver to her collection.
But it will be extremely tough for the Brit to overhaul the seemingly unstoppable Nafissatou Thiam - the reigning world and Olympic champion.