Like any big, busy city, it can be quite hard to make friends in London. That doesn’t mean it’s not possible. It just means you maybe have to put a bit more effort into it. University and work are obvious starting points, as is the pub and the gym, and there’re tons of clubs, activities, classes, etc. all offering opportunities to meet new people if you want to. There’re also, of course, many things that you can do by yourself and may well want to do so!
Meetup is an excellent site where it’s possible to find and join groups which hold events centred on a particular interest. The groups vary in level of organisation, but there’re thousands and thousands to choose from so I’d be surprised if you couldn’t find something that interested you. Some of the categories include the outdoors, health and fitness, photography, cooking, the arts and languages, but there’re many others.
TimeOut offers a useful guide to the city and will be familiar to many people, but I personally find Secret London more interesting, as it covers quirkier and less well-known things to do around London. As a starting point, check out Secret London’s 500 of the Best Things to Do in London.
Saving money is likely to be of interest to a lot of people, so also check out Secret London’s 200 Fantastic Free Things to Do in London. Museums, parks/walks, markets, lunchtime recitals, etc. are all free and there’re often discounts available on everything else. There’re lots of affordable eating options. People, of course, will have different interests, but art lovers might be interested in the National Art Pass, and theatre lovers in TodayTix, which has ‘rush’ and ‘lottery’ opportunities for same-day theatre tickets.
This was only designed as a very brief introduction to London, but I hope you’ve found it useful in some way. Let me know if you have any questions.