How you respond to that first call to service may very well set the pattern for the rest of your life. Respond rightly and God will build upon it. There is no telling what He will do with you!
If you want to serve God then start by doing the little things. Pray about it, be a soul winner, and serve in the church even if it involves menial activities. You will be amazed when you see how He works these things into your life and issues a call to you!