Be realistic about...
Acknowledge their expertise, and make them partners in creating an effective learning environment in your classroom.
Involve your LSA in curriculum design and target-setting. They will know what's realistic. Conversations along these lines will help you work out each other's roles and responsibilities. Take their advice about the learning styles of the pupils in their care - they know what works, and will help you differentiate your materials.
Use what they know about their pupils' challenging behaviour. They are not there to sort it out, but they will have seen and can tell you about successful management strategies.
Make sure that they are included, as part of the team, in your departmental training. The more they know about your approaches and materials, the more helpful they will be.
Include them in the praise you give their pupils. Support them when things don't go so well.
Above all, listen when they talk about "their" pupils; they probably know them, and their families, far better than you ever will.