Part of any good relationship is knowing when to talk and when not to talk. This is relevant to a good conversation too.
Read the Conversation
Make sure when trying to get a date, talk to someone that you are aware of the conversation and how the other person fits in.
A good conversation should not be totally one sided. Don't always talk about yourself as the other person may get bored.
Some people will be more willing speakers than others. Try recognize if you are a person that talks too much. Perhaps that is natural for you or you only do this when you are nervous. You can still be yourself, but also be considerate of your date.
If they are not openly trying to add things to the conversation, they may be a bit shy, or not know much about what you are talking about.
Ask Open Ended Questions
Perhaps you can ask them some questions to try and get them into the conversation. Good questions are open ended, ie, not a simple yes or no answer. If you ask a person an open ended question then they will have to think about it and give more than a one word answer. Be sure to listen to the answer and perhaps ask another related question.
Get Into the Conversation
If you are on the other hand and are not doing much of the talking, perhaps you need to stop nodding (either asleep or with your head) and start asking some questions or adding your own theories.
Is the Conversation Focussed?
Try to read the conversation. If your dates eyes are glazing over, you perhaps you are not in the right topic, or have been on it for too long.
If you are not a natural at conversation you can prepare some questions you can fall back on to kick-start a conversation.
Conversation is an art that gets better with practice and some thought.