How to seize this guy who I met through online dating service?

We met through an online dating service. We have exchanged about 15 emails (very long ones) so far. We went out for dinner last weekend. He is not hot by any means, but very intelligent and considerate. I really like him and want this to turn into a relationship. However, I am not sure how to approach this. He seems to be interested but has not been very assertive. I want to talk to him more, but I don’t want to be seen as desperate or anything. What should I do? Help!!!