The guiding hand might suggest someone who has a great influence on you. A mentor, coach, friend, or parent whose guidance has helped to shape your life.
A missing link could be some aspect of a person's life that is missing. In reverse, you could speak about the idea that without this aspect of your life you are incomplete.
A stepping stone would suggest one level of the journey toward the goals that you hope to achieve.
When writing a speech, it is important to have the one main claim you are making....the argument...or point you are trying to make. Then everything else in the speech pertains to that statement.
In your introduction, you begin with a brief attention getter...quotation, illustration, etc., then, you state your claim. For example, after having told a brief story about your coach, you then go on to say that without his influence, you would not be majoring in physical education today. Each following point would prove this statement.
Remember the old saying about a speech:
Tell them what you are going to tell them....(Introduction)
Tell them...(of course, here you are going to have to give some examples, reasons, anecdotes, and illustrations)(Body)
Then, tell them what you told them. (Conclusion)
It works every time.