People in England should now aim to wear face coverings on public transport and in some shops, the UK government has said.
A document outlining new coronavirus lockdown rules suggests face coverings for enclosed spaces where social distancing is not always possible.
People are also allowed to meet one person from another household outside.
It came after Boris Johnson announced on Sunday a "conditional plan" to begin lifting England's coronavirus lockdown.
Scotland, Wales and Northern Ireland have their own powers over the lockdown and have not lifted measures to the same extent.
The PM led the government's daily Downing Street briefing after appearing before MPs in the House of Commons.
Mr Johnson told Parliament the "roadmap" for lifting the lockdown would enable the country to "control" the disease if people continue to follow the rules.
He said the public should exercise "good, solid, British common sense" in adapting their lives to the next phase of the coronavirus response.
But Labour leader Sir Keir Starmer told the Commons the country needed more "clarity and reassurance" from the government, and that "both are in pretty short supply".
He later added: "The prime minister said he was setting out a roadmap, but if we're to complete the journey safely a road map needs clear directions. So many of us have questions that need answering."
It comes as a further 210 people have died in the UK after testing positive for coronavirus, taking the total number of deaths recorded to 32,065.
After eight days of missing its goal of 100,000 tests a day, on Monday the government counted 100,490 tests on 10 May.
Sir Patrick Vallance, the UK government's chief scientific adviser, told the Downing Street briefing that Office for National Statistics data suggests an estimated 136,000 people are currently infected with coronavirus in the UK.
He said the amount of time it may take for this number to halve is around two weeks on current infection rates.
The government published a 50-page document on Monday afternoon, alongside new guidance for the public, setting out more details of its planned timetable for lifting Covid-19 restrictions.
"As more people return to work, there will be more movement outside people's immediate household," the guidance says.
"This increased mobility means the government is now advising that people should aim to wear a face covering in enclosed spaces where social distancing is not always possible and they come into contact with others that they do not normally meet, for example on public transport or in some shops."
The new guidance makes clear that a face covering is not the same as face masks, such as those worn by healthcare workers which "must continue to be reserved for those who need it".
Public Health England has published an online guide, detailing how to make a cloth face covering.
Other countries have already introduced rules about wearing face masks, however the government in Wales said it was not going to make wearing face coverings mandatory.
Welsh First Minister Mark Drakeford said the evidence was "not strong enough for that", but people could choose to wear them if they wished.
The Department for Business, Energy and Industrial Strategy has published guidance for companies "to help them get their businesses back up and running and workplaces operating as safely as possible".
It features a number of suggestions, including carrying out a workplace risk assessment with trade unions, maintaining a 2m distance wherever possible, and "reinforcing" cleaning practices.
'We will have to learn to live with risk'
As we gradually move out of lockdown, we are going to have to accept we are living with more risk than we once were.
There is, after all, a virus circulating - that is infectious and can be deadly.
The government is taking steps to try to minimise that risk (and of course there is plenty of debate whether it is doing a good job) as well as asking us to play our part by following the guidance, not just for the sake of our own health but also the health of others.
But how high is the individual risk? What's become clear since coronavirus emerged is that the most at risk are those with vulnerabilities.
Latest data suggests 1% of deaths in hospital in England involve people under 60 with no underlying health condition.
Factor in the care home deaths, which are accounting for growing numbers of fatalities, and the overall proportion will be even lower.
That is why the government is asking those with health conditions to be more stringent, including for some, continued isolation, which is incredibly tough to do.
But for the "healthy population" it is clear the personal risk of dying is incredibly low.
The younger you are, the lower the risk. For the under-25s, statisticians have likened it to the risk they would face from dying from several days of normal life - there is always the chance you could have an accident or suddenly die.
But it is not zero - and that too can be difficult to live with when we are so aware of it.
From Wednesday, people in England will also be allowed to meet one person from outside their household as long as they stay outdoors and stay 2m apart, the advice says.
Sage, the government's group of scientific advisers, says the risk of infection outside is significantly lower than inside, according to the document.
The guidance also said the government's ambition was for all primary school children in England to return to school for a month before the summer.
But asked during the Downing Street briefing what people should do if they do not have access to childcare and cannot work from home, Mr Johnson said he was sure employers would be understanding.
"If people don't have access to childcare and they have a child who isn't back in school then I think that's only fair to regard that as an obvious barrier to their ability to go back to work and I am sure employers will agree with that," he said.
Meanwhile, the new guidance confirmed garden centres will also be able to reopen on Wednesday with distancing measures in place.
It is likely that the government will continue to advise people who are clinically extremely vulnerable to continue to shield beyond June, the document adds.
And the document also says:
- People in England can drive to any outdoor open space in the country - but not to other UK nations
- Team sports should not be played - but people can exercise with up to one person from outside their household
- Healthy people aged 70 and over should take particular care to minimise contact with others - even if they have not been advised to shield by the NHS
- Clothes should be washed regularly if people work with others outside of their household
- Doors and windows should be left open in places where people from different households come into contact
- There needs to be "a rapid re-engineering of government's structures and institutions" to deal with Covid-19
Fines for those who do not follow the rules in England will increase from £60 to £100 from Wednesday, with maximum total penalties for repeat offenders of £3,200.
Speaking about potential future measures, Mr Johnson told Parliament the government was exploring how to safely allow people to expand their household to include one other "on a strictly reciprocal basis".
The guidance also sets out the government's three-step plan, announced by the PM on Sunday night.
All dates could be delayed if not enough progress is made in tackling the virus - and restrictions could be reintroduced, the guidance says.