Top 3 methods that worked for me:
1) Smile and say greet them with a "hello", "Good Morning" "Good Afternoon" etc. as appropriate. They may look at you sideways for a bit, but they'll warm up to you.
2) Join workshops and groups that focus on activities you enjoy. This opens a door for sincere communication on a mutual interest.
3) Volunteer. You'll meet a LOT of decent folks to befriend, ranging from low-income families with good hearts to high-powered business folks who want to give back the community they love and those in-between.