Real life and writing correlates quite a bit, even if you’re writing fantasy, for example. Obviously, you’re writing in a language you know, so there’s a point – you’ll probably use your own language tics in your work (such as the main character dropping articles, for example). Your characters are probably also influenced by people from your real life and conversations. Have you ever read a character and thought, “Hey, my friend does that…”?
Obviously you can’t completely copy people in your real life – there’s probably a law against it, or something, and you wouldn’t be creating your own characters. But, there’s nothing against you using aspects of people around you in your writing. If your friend has a really funny sneeze, or they have a catchphrase that they say all the time, then why not magpie it and use it in your own work? Even if they noticed, they’d probably be happy that you thought that that part of them was good enough to be used in your novel!
Bit how do you know what type of stuff to take and what type of stuff to leave? Well, you can keep a writing journal, obviously, and write down everything (a really great exercise for this is sitting in a coffee shop or on a train for example, and writing about the people around you). Then, you can flick through and find out the things that best fit your characters. Alternatively, you can just notice around you, and write it down later. Or, not write it down at all, and hope you’ll remember! If you use something in a close friend, you’ll probably know it anyway.
Even if you don’t write anything down, you probably will realise that some aspects of people around you in everyday life will come through in your own work subconsciously. This isn’t a bad thing! Even published writers are still influenced by people around them – take JK Rowling, for example! Besides, it gives you some great ammunition for writing and it means your characters are likely to seem realistic to the reader, because they have characteristics from real people!
Therefore, using real life people in your writing is a pretty good idea – just, don’t copy them completely. Otherwise, I guess you’re writing fanfiction about your own life… now there’s something for you to think about!