For me when I'm on the trails and approaching a hill I remember reading somewhere before to yell out 'rider up' as you take a hill and before you decend a hill you ring the bell to alert anyone below of your decent and decend slowly is it's twist and winding so incase a rider is coming up you can avoid them.

When I see people with pets I always ring the bell or verbally warn them in advance then pass them slowly (normally on the left hand side) while keeping an eye on thier pet to make sure they don't freak out and chase you.

For walkers and joggers I always ring or give a yell 'passing on your left/right' and if the person acknowledges your call with a wave or 'thanks' I give a wave back as I pass them as a 'thank you'.

Most of the times when riding on the road I only wave to other riders on the road.