Mrs May said President Trump shared some of her political values - including that of Brexit Britain.
The British Prime Minister has said the UK won't back away from its condemnation of the use of torture - no matter what approach Donald Trump takes.
Theresa May also said she aims to charm Donald Trump into backing a trade deal, declaring that "sometimes opposites attract."
Mrs May believes she will be able to endear the US President into backing NATO, the UN - and even the EU.
Speaking to reporters on her flight to the US, Mrs May said President Trump shared some of her political values - including that of Brexit Britain.
She said: "I think we both share a desire to ensure that governments work for everyone and particularly that governments are working for ordinary working class families.
"I think that's important. That's what I've spoken about.
"I did it on steps of Downing Street when I became Prime Minister; a country that works for everyone and an economy that works for everyone.
"I think we share that interest and that intention in both our countries."
Asked ahead of her White House meeting on Friday about the contrast between a vicar's daughter and a reality TV star, Mrs May joked: "Have you ever noticed that sometimes opposites attract?"
The PM is the first foreign leader to visit the Trump White House and said she was pleased to be going "so early" in the administration.
Mrs May declined to criticise the President's crackdown on immigration.
She said: "The rules that the US introduces are rules for the US."
She would not be drawn on his controversial claims about millions of illegal voters.
"What happens in US elections is not a matter for the British PM. It is a matter for US and US authorities," she said.
The PM also signalled a significant toughening on the language around Iran's nuclear deal, signed in 2015. President Trump has suggested scrapping it.
Mrs May said: "I think it was an important deal that was done and I think it is important that we ensure that the deal is properly enforced."
Mr Trump, during a speech to top Republicans, said he would be doing the negotiating with the UK:
He said: "I'm meeting with the Prime Minister tomorrow, as you know, of Great Britain… I don't have my commerce secretary and they want to talk trade… so I'll have to handle it myself, which is okay."
During the speech he set out the US approach to trade deals: "Believe me, we're going to have a lot of trade deals. They'll be one-on-one. They won't be a whole big mash pot.