When your partner serves, you are already part of the first attacking pattern. Your position should support the serve and prepare the pair for the first volley.
Standing in a connected net position helps you cover your half of the court and reduces the space through the middle.
What to do
Your role is not to chase the serve or drift away from the point. Stay ready, watch the return and be prepared to handle the first ball that comes through your side or the centre.
As the server moves forward after serving, the two of you should become a connected attacking pair rather than two players occupying unrelated positions.
Why it works
The important idea is pair shape. The partner starts ready at the net, the server joins, and both players prepare for the next ball.
That creates a much clearer first pattern than one player serving while the other stands without a defined role.