The Grove outfit is currently enduring a difficult 2019 campaign, as it has been consistently stuck at the back of the field for the entire year.
Russell believes that the FW42 has improved "a lot" throughout the year in terms of driveability, and thinks that strong foundations for the 2020 season are being laid down.
"It’s definitely improved a lot, just in the driveability side of things," the Briton said. "So, from within, it’s definitely a nicer car to drive.
"It is obviously, always difficult to make huge leaps forward for any team but I think the foundations we have in place now are really positive going into next year.
"We’re trialling a new front wing this weekend, which shouldn’t necessarily bring much performance to this year’s car but should hopefully unlock quite a lot for us moving into 2020, so I’ve got faith we should be fighting.
"Probably towards the lower end of the midfield but hopefully in the mix much more than we are at the moment."
With just five races remaining in his rookie season, Russell says that he wouldn't change anything despite the tough year for Williams, as he believes that he has learned a lot through the difficulties.
"I wasn’t 100% sure what to expect but I’m really happy with how the season has gone generally. From the good moments personally to the tougher times I wouldn’t change anything at all.
"Especially from the tougher times I’ve learned a huge amount and generally being in the position I have been, at the back of the grid, it’s given me an opportunity to just explore a bit more and go under the radar and hopefully that will help me out in years to come when we should be fighting."
Bahrain International Circuit - Winter testing