The people of England, like their language, are a mixed bunch who have regularly been infused with new blood - from the Romans nearly 2000 years ago taking control of the ancient British in the region, to the later influences of Angles, Saxons and others from Europe after which created the original idea of the English, to the Vikings and then the Normans about a thousand years ago. Since then, there have been Hugenots, Chinese, Jews fleeing pogroms, people from former British colonies in the Caribbean in the 1950s and 60s, Indians expelled from newly independent former African colonies, workers from new EU member states such as Poland, not to mention people from other UK nations and the Republic of Ireland. The full list is very long, but England has long been used to outsiders making it their home - even before England existed! It is true to say that not all English people welcome foreigners and some distastefully racist political organisations exist, but it's a very small fraction of the population who subscribe to such views. Almost everyone will treat you well if you are polite and make an effort to fit in. Smile, be polite, don't be pushy if you can help it: that's how to get on with the English.
The English are also well used to foreign visitors and you can expect them to be friendly and polite. One thing to bear in mind is that many mostly elderly English people are terrified of giving offence and dislike lying, and so will try to avoid potential pitfalls by sticking to safe (often boring) topics of conversation and occasionally doing the tricky job of avoiding offence by evading a question which worries them, while also trying not to offend you by point blank refusing you an answer. This sort of thing generally wears off as people get to know you. The younger generation are often quite different as far as giving offence is concerned.
Big cities and even some rural areas, like those anywhere, have their social problems, but England is predominantly an affluent country with little visible poverty. Rough areas contain rough people in England as in any country: muggings, car theft, and other street crime are unhappily common in some districts of many towns and cities, but England is by and large a very safe country as long as you use your common sense.
In tourist destinations you will meet a mostly friendly people who will take the time to answer a stranger's question, and who may speak English in a colourful or accented way but will be willing to standardise and simplify their speech if you're struggling. Some would say there is a north-south divide, with people in the North more friendly and approachable, while the South (mostly just London though) is a more closed culture with people less willing to stop and speak, but don't take offence, remember most Londoners you see on the streets will usually be rushing to get to somewhere (eg work) and simply don't have the time to talk. However in rural areas of the south, particularly East Anglia and the West Country, people are generally much more laid back and enjoy taking the time to have a chat with strangers. In most of England you will usually find that if you are polite and friendly, you'll get the same in return.
London itself is a very international city where you may meet a variety of nationalities, depending on what part of the city you are in.