Even as she makes behind-the-scenes preparations for her potential administration, Hillary Clinton on Tuesday warned against complacency among her supporters and urged voters to ignore all polls that show her beating Republican Donald Trump.

At a campaign rally in the crucial swing state of Florida, the former first lady conceded that her campaign is confident about its prospects. In recent days, Mrs. Clinton and her top surrogates have focused much of her attention on down-ballot races, and the Democratic nominee also reportedly has been calling Republican leaders on Capitol Hill to begin rebuilding relationships there.

But Mrs. Clinton seems keenly aware that overconfidence could spell trouble for Democrats and could derail a potential landslide win, or prevent her party from capturing control of Congress.

“We still have a lot of work to do. I feel good, but boy, I am not taking anything for granted,” she said. “I am going to work as hard as I can between now and the election two weeks from today. … Pay no attention to the polls. Don’t get complacent because we have got to turn people out.”

Mrs. Clinton leads Mr. Trump by 5 percentage points, according to the most recent Real Clear Politics average of all polls. Other surveys have given her a larger lead.

In addition to turning her stump speeches into get-out-the-vote rallies for down-ballot Democrats, Mrs. Clinton and her campaign also have redirected millions of dollars to House and Senate candidates, hoping to secure a Democratic majority in the House and Senate.

The campaign also reportedly is spending more time building a transition team that would go to work immediately after the Nov. 8 election.