The answer depends on your current strengths, also please consider most of these are related
and difficult to master as a separate item or discipline.

I suggest you have a solid base in the following order.

Option 1. Good listener 
- This will automatically help develop the remaining skills, they are reliant on it.

Option 4. Committed and reliable.
- Trust and respect are crucial for team building and leading by example.

Option 3. Patient and encouraging.
- Learn to balance performance expectations with empathy and understanding.
  However, sometimes a mentor must be tough but fair, strive to know when.

Option 2. Knowledgeable and experienced.
- To some degree, if you are ready to mentor the knowledge will be there. 
Many mentors overvalue technical ability and are less relatable.
That said, you still need to intimately know your subject matter 

Option 5 - Role model
- By working through the other points, this is inevitable.
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