As a follow, your part in the partner dance is to take the energy/momentum that your partner gives you, carry it through your body and embellish it. How you hold your body is important to give you the best chance of feeling and responding to the momentum your lead is giving you. So I would like to propose the concept of 'yielding' to help you understand the way to do this. In yielding we let go and become immersed in the experience that is facing us. This is in contrast to resisting or controlling.
When I stand with my partner, even before we've begun dancing, I yield myself to my partner, and what this looks like is relaxing into the physical hold that we have. I let my partner take the weight of my hand and I relax into the arm around the back, or any other places that we make a physical connection. Just like you might do if you were hugging someone. You don't collapse your whole weight onto them, but connect with them in a soft, gentle way, letting them know that you are there and receptive to what they're going to bring to the dance.
In my work teaching dance, I find this a difficult thing for follows to allow. I feel it is in large a reflection of society always asking us to be 'on', 'ready' and in charge of everything we do in life. To be controlling of the outcomes we want to see instead of allowing the flow of where life is taking us. This is a huge teaching partner dance can provide, but once that teaching has been realised, there's pure pleasure in yielding to the dance as a follow.
Like the flow of a river, let yourself be carried away with the momentum the lead is giving you.