The exercises elsewhere on this site and your own thoughts and experiences will hopefully result in a list of candidates of Life Purposes.
If you have no candidates at all you may need to discover and confront what it is that you fear. Your fears may be preventing you from finding your true Life Purpose. In the absence of fear each living being naturally exists in a state of becoming and has desires and hopes.
If, on the other hand, you have a healthy list of candiates it may be advantageous to put them in writing. I like to use a small whiteboard. I prefer a white board over paper or a computer list because a white board can't get lost or be forgotten. In any case, the act of writing forces a final refinement of your purpose candidates and gives you a chance to clarify what it is that you want.
Let that candidate list sit and gel for a few days and make certain you haven't overlooked anything important.
When you are convinced that you have explored all candidates of interest to you, its time to make a choice. If the decision is difficult see More Decisive.