All the ideas from MrScott are very good indeed.
In general, I’d say, to build new friendships:
follow your interests (via Meetup.com etc. ),
volunteer your time/work at or for places/causes that you enjoy,
join OR create a club for your interests – even if it is to get ADD /ADHD folks together for a chat (all of the above as MrScott says);
and: reach out to others wherever your interests take you (walking your dog? go to a dog-park … lots of like-minded folks there).
Some things that I’ve learned the very hard way:
>Never make assumptions ( e.g. “that person has 4 kids, I only have a dog -there’s nothing in common” ; you never do know; perhaps that person always wanted a dog, but cannot, because of the 4 kids being a lot of work).
>Give it a lot of time
>To give-it-a-lot-of-time, without hitting dead-ends, start many, many attempts at meeting different people – say, 100-200 potential friends per year. Then a small percentage of success will give you great rewards, and you’ll have lots of practice and be getting better. Try and pace yourself – when strong & enthusiastic, keep at it, so that you compensate for low-energy periods when you cannot reach out.
> PLAN AHEAD ! ( You can’t call ‘friends’ for a get together, without some advance time – at least several days).
>If you think you have unique/strange/foreign interests, those are great attractions to lots of people looking for companions in those unlikely interests.
(Not many of my friends like bowling – perhaps they’re not good at it, or think it is too ‘middle class’ or whatever – I make no assumptions – but I still look for those who want to go enjoy bowling.) Don’t ignore what makes you unique.
>Pursue all your interests – there is no time to ignore any of them
Hope this is helpful.