I make friends easily. I think what it is is that I am interested in other people and ask about them and their interests - even if they are not mine, I can still show interest in what makes another person happy. It is surprising how many people can only talk about themselves and what interests them. In my experience, those people are also the people who think that others aren´t quite as good as they are - and that is an unattractive trait in a friend.
I also think I have a lot of friends because I hardly ever feel slighted. A lot of the things people write about on MN as rude or grabby or whatever, wouldn´t even register with me. People are fallible. Sometimes we all do and say stupid things. I don´t dwell on it.
Also, being able to chat away does help as it is easier to be socially with someone who will talk back. But I have plenty of shy friends too. Often it is easier to do some specific activity together rather than just go for a coffee. It fills the silences and doesn´t leave the weight of the conversation on one person.
So my suggestions for finding and keeping friends are: be genuinely interested in other people, do not look for slights and reasons to be offended, be generous towards your friends if they don´t always behave exactly as you think they should, and find activities that are suitable for you and your friend to do together.
Also, take your friendships lightly. Don´t overthink, don´t be needy, don´t worry about them. Just take them for what they are there and then. If someone is suddenly busy, don´t think that it is you and that you have upset them. Just think that they are busy. Go talk to someone else for a few months and then contact your friend again. Whatever you do, don´t turn it into a big, intense conversation about your friendship.