It's random, so I try to help if the situation arises.
If I see an opportunity I try to take it, and not worry about the ones that I miss. If I were to give myself a quota, it'd probably be one act of kindness every Friday as King Danny has advised, but I feel that forcing myself to be kind would only stress myself out more. Gotta help yourself before you can help others!
I don't goal it, but I do try to treat people well every day. I'm the kind of person who holds the door open for others. Lets you cut in front of me in line at the grocery store if you seem like you're in a hurry. Sometimes even a simple smile is a random act of kindness! =)