1) Don't be a litter bug. I believe there is a negative butterfly effect caused when people drop litter on the floor. If someone was a tourist and saw a small pile of rubbish on the floor they could return to their homeland and tell their friends that England is a dirty disorderly place and that would put off other tourists from visiting. The other problem would be rats, you could help to cause outbreaks of a disease and things like that.
2) Visit Piers from time to time. One thing that makes the Island of Great Britain special is we have a very high concentration of piers for our size. If you go on a day trip to the coast, visit the pier knowing the toll they charge or the money from a cup of tea will go towards maintaining and improving the pier. Have a coffee or Tea sitting on a Pier.
3) Buy British: If you can, buy things that are made in Britain. Buy tomatoes that are grown on British farms, buy t-shirts that are made in British factories.
4) Be Nice: it will cause a ripple of goodness that will spread through the country. You don't have to do favours for people, you can just return a greeting or not have an angry outburst when someone making you feel impatient.
5) Know our good history. We did bad things in the past but we also did good things that should merit some pride. Some people only want to talk about the bad things Brits did in the past. There are countless innovations and medical breakthroughs that occurred right here in Britain. The world condems slavery because of Britain and we pioneered democracy.