Sitting in front of this page, despite a deep calling and inspiration, I find myself at a loss for words. This might be in part because of the broad nature of the topic as well as it's depth. What comes to mind is a talk I heard years ago: someone asked a "birthday" question....and the resulting talk about selfless, about perfect service.
For those truly interested, I highly recommend listening to it. There is also a book that comes to mind: "The Joy of Sacrifice".
If you are progressing on the spiritual path into the higher evolutionary levels, serving and service will eventually come up. You WILL have to face what it means, what it means for you, what form it takes in your life and then, what selfless service is, ->! consciously entered and committed as a way of life, as a practice. You will have to come terms with service and necessary self care, and what that means at any given stage, to continue the service. If you are not on this path, don't worry. You need not concern yourself with these matters. If you are reading this however, chances are you higher conscience has already received a wake up call, you already intuit, and in fact KNOW, you have been called. Then it becomes a matter of: what do I do now, what can I do next, where do I turn? If you have come this far, you already know of the importance of regular practice, whether you are able to stick with it or not. You already know of the helpfulness of a spiritual community, the sangha of like-minded people on the path, can be. You already know that you need help and have to learn how and when to ask.
In the practical application of the Way of Service, there are many available tools to help in this process. One very practical is using the Red Bag of Courage approach, or, as I prefer to call it, The Red Bag of Service. Another very useful and interesting tool is: Learning to play Zen Flute - which in the end is Service to the Flute. As with so many things, it is what you will in fact apply yourself to consistently which will make the difference.