The last handful of seasons has seen the energy drink squad start the season off on the back foot before getting more competitive towards the end of the season as it develops the car.
With stabilisation in the 2020 regulations before a major switch-up in 2020, Red Bull will be hoping that it can start next season on the front foot.
However, Verstappen sees that to be a challenge for Red Bull, despite the strong race and qualifying pace that it displayed in the second half of 2019.
"It depends a bit on the layout of the circuit, but for our part, we've made some good improvements during the season," Verstappen said.
"It allowed us to fight a little more at the front and win a number of races. But there is still a lot of work to be done next year to catch Mercedes.
"In the end they have been the dominant team, or at least the most consistent team, over the whole year. We will try everything we can to close the gap, but of course that won't be easy."
Verstappen picked up three race wins during the 2019 season, the most he has ever won across a single campaign.
He also bagged his first pole position at the Hungarian Grand Prix before the summer break, which remains his one and only pole following his penalty in Mexico.
Bahrain International Circuit - Winter testing