Begin pointing out your strengths and weaknesses and compare them to you spouse or other adults in your child's life. Find things your older child does well and compare them to your weaknesses. Create an atmosphere in the home that it is normal for everyone to have different abilities at different things.
Focus on rewarding effort not outcomes. When a gifted child does well without trying hard don't praise and reward their lazy achievements.
For a long time your older child will be physically and emotionally more talented than your younger child. Explain how she can be gracious about being older, stronger, taller, etc. Keep it concrete. And anticipate that she will use her elder status to influence, punish, and control her younger sibling (as in all sibling rivalries). Set a strong tone that criticizing others talents is foolish and wrong.
Be honest about differences and play to each child's strengths.