Appearance
Choose a visual style and an adult age. Decide which details should stay consistent: hair, eyes, clothing and a few recognisable features. A short, specific description is easier to work with than a list of unrelated traits.
Personality and background
Give your companion a point of view and something to talk about. A profession, an interest and a current problem can do more for a conversation than several broad adjectives. Describe how they respond when they are curious, uncertain or challenged.
The first meeting
Write the opening in a place and at a moment that fit the character. Leave a question or decision for the other speaker rather than writing their response for them.