The three-times champions were drawn on Saturday along Thailand, Sweden and debutants Chile in Group F at the 24-team tournament starting in June.
Under Ellis, the Americans swept aside their rivals to win the World Cup in Canada three years ago, most memorably in the final when Carli Lloyd scored a hat-trick in a 5-2 thrashing of Japan.
The English-born 52-year-old said they had set up friendlies against top-ranked sides such as Japan and Brazil to stop any complacency setting in.
"I’ve got a tremendous staff and we will start to zero in on these teams," Ellis told reporters at the Seine Musicale in Paris.
"We’ve set a really competitive schedule for us in the next six months and I think that’s going to give a lot of answers and let us try a lot of different things," she added.
"I feel like we’re going to be battle-tested going into this World Cup with the schedule we’ve planned."
Ellis pointed to the contrast in styles of the teams they face in friendlies which correspond with their World Cup opponents. The U.S. begin 2019 by facing tournament hosts France in Le Havre, one of the nine World Cup venues.
Despite having serial winners such as Alex Morgan, Lloyd and Megan Rapinoe in the side, Ellis said the veterans of her squad still look for ways to improve.
"For us, it’s still about getting better and better and this is what these players are excited to do and I think if you asked any of them they would say ‘yes we’ve done well, but we can be better’ and that’s an exciting mindset for these players," she said.
The U.S. begin the defence of their World Cup title against Thailand in Reims on June 11. (Reporting by Christian Radnedge, editing by Ed Osmond)
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