Form the image of Radha and Krishna, or if it's easier for you to think of only one of them, then you could think of just Radha or just Krishna. Or if you like to think of both, then think of both. Think of them not in the way that you're imagining someone at a distance, but actually visualize them as if your eyes were open and you were meeting them face to face.
It should have that kind of real feeling. We call this bhagavad bhavana, imbuing our meditation with this faith that real Radha and Krishna are here with us. In fact, they even inhabit the form that we are imagining because they pervade everything.
This is the essence of Roop Dhyan. Imagine Radha-Krishna and imbue that imagination with faith so that it's no longer imagination, but you're trying to actually see real Radha-Krishna right here in front of you.
And since it's real Radha and Krishna, you can see their eyes moving, their eyelashes moving, their ear pendants slightly jiggling if they move their head.
You can see their chest rising and falling as they breathe. You can see them smile as they look towards you. You can even hear them say something to you.
