I really think the key in seva, charya stage in Saiva Siddhanta, karma yoga, selfless service, or whatever we call it is to focus on the other person, or people, and not on ourselves, and most especially not on our own spiritual progress or accomplishments. That takes care of itself, if we're not self-centered.
Here's a simple example I saw today. I was in the express line at a store, and there was a li'l ol' lady right in front of me. She was having trouble with all the machines, the credit cards, put in the wrong one, and all of that. Seeing that the customer was frustrated, the teller said, (a white lie, I suspect) "Don't worry, Ma'am. I'm far worse at that than you are." So that was the choice the teller made. Focusing on the other person, and alleviating the stress in her. Surely there were no thought of reward in that simple action. The teller used her free will, in that moment, to make the dharmic choice. The other choice would be to scold, or look angry and irritated at the ineptitude.
So then of course I had to open the silly mouth and say, "I'm far worse than either of you, cause I'm a man." Smiles all around, and the three strangers feeling better about how the rest of the day might go.