The easing of lockdown rules in England is the "biggest step yet on the road to recovery", the prime minister has said.
Many businesses - including pubs, restaurants, hairdressers and cinemas - can reopen from Saturday.
Boris Johnson said the public "must not let them down" by being complacent about social distancing, and he would "not hesitate" to reimpose restrictions if the number of Covid-19 cases rises.
"Targeted local" measures would replace "blanket national" ones, he said.
England's chief medical officer, Prof Chris Whitty, who spoke alongside Mr Johnson at Friday's Downing Street briefing, said no-one watching would think the easing was a risk-free step but that "there is no perfect, exact way of doing it".
He also warned of the risk of coronavirus spreading in pubs.
"There's no doubt these are environments whose principal job it is to bring people together. That's a great thing to do socially, but it's also a great thing from the virus's point of view," he said.
"And therefore we do have to have a really clear and really disciplined approach to try and maintain social distancing whilst also enjoying pubs."
Mr Johnson said: "The success of these businesses, the livelihoods of those who rely on them and ultimately the economic health of the whole country is dependent on every single one of us acting responsibly."
"We must not let them down," he said, adding that he wanted people to "enjoy summer safely".
Pubs have been told they must wait until 06:00 BST to reopen as a "precaution" to avoid midnight parties.
And pub-goers are being encouraged to book tables in advance, while live gigs and standing at the bar will not be allowed.
The 35,000 or so pubs and small bars trading in England have been closed since 20 March - a day when 645 positive coronavirus cases were announced.
On Friday, 544 new coronavirus cases were announced, the lowest daily figure since 17 March - while there were 137 further deaths confirmed, taking the UK total past 44,000.
As well as the easing of restrictions on the hospitality industry, social distancing rules will change from 2m to "one metre plus" - meaning you should take additional precautions when people are within less than 2m.
The rule changes come days after a local lockdown was put in place in Leicester because of a spike in cases, with residents advised not to travel and businesses and schools remaining closed.
Mr Johnson said "good progress" was being made towards the reopening of other businesses - such as gyms, nail salons and night clubs - and that a timetable will be set out next week.
Outbreaks of coronavirus are inevitable.
The virus is now at much lower levels, but it has not gone away and may never go away. Until we have a vaccine it will always pose a threat.
We have already seen outbreaks in Leicester, Weston-super-Mare and Kirklees. Relaxing lockdown will make them more common.
Remember, this is a virus that thrives on close contact - the more people we come into contact with, the more coronavirus will spread. It was true in March, when lockdown came in, and it is true now.
However, outbreaks are not a massive problem as long as they can be contained.
If they can be spotted and rapidly stopped then an outbreak may cause local disruption, but not "National Lockdown Two". This will be the challenge for NHS test and trace.
However, some scientists are concerned lockdown is being lifted too quickly and that we are not yet able to stay on top of the virus.
The danger is failing to stop an outbreak could lead to coronavirus spreading widely and cases surging.
During the briefing, the prime minister laid out a five-step approach to tackling local outbreaks.
This will involve authorities monitoring data, engaging with local agencies and carrying out testing.
At the fourth stage, targeted restrictions, Mr Johnson said activities will be restricted "at particular locations" with "individual premises" made to close.
The final stage would be a local lockdown, which he said would be "carefully calibrated depending on the scientific circumstances of each outbreak".
Prof Whitty said the country would see both health and economic problems as a result of the pandemic and the government was trying to "walk this narrow path".
"What this is is an attempt to balance, as best we can, in a way that makes it possible for society to be as close as possible to normal, whilst living alongside this virus - which we will have to continue to do," he said.
He added that there is a "real possibility" of a second wave - which "goes up sharply" if people do not take social distancing measures seriously.
"This possibility will exist with us for a very long time, so we have to prepare for that," he said.
"The best thing to do is to make that as unlikely as possible."
What about the rest of the UK?
Each UK nation's lockdown measures differ, including varying rules on the reopening of food and drink outlets.
In Northern Ireland, pubs and restaurants could reopen on Friday.
In Scotland, beer gardens and outdoor restaurants will be allowed to reopen from 6 July, and indoor areas can be used from 15 July.
The Welsh government has promised talks with the hospitality sector about a "potential phased" reopening, but no dates have yet been given.
The Department of Health and Social Care said 44,131 people had died in hospitals, care homes and the wider community after testing positive for coronavirus in the UK as of 17:00 on Thursday - a daily rise of 137.