Hi Rikki,
In creating most of my intros I do the following:
1. Decide how many measures I want in the intro (or ending).
2. Then assign the desired chord structure to the measures.
3. Create a melody line that will fit the chord structure, allocated measures, and the attributes of the particular song and instrumentation.
4. Decide on the instruments to use.
5. Record the lead part of the intro.
6. Add appropriate accompaniment.
Seems like a lot to do, but it goes fast and fits whatever song I am working with.
Happy hunting.
Larry