So many experts are clamoring about whether to make yourself busy or be available. Each one gives opposing advice which practically makes it impossible to definitively know which approach is best. Thus, I am going to attempt to lay out the answer in the most clear, precise, and actionable way possible.
First, whether you are in a relationship or single, build the best possible life for yourself. What does that mean?
Have balance between the 6 pillars of Happiness.
Most importantly, realize that one person is not going to be able to provide you with everything you need.
So back to the question at hand, should you be busy or available?
The answer is you need to build a lifestyle that is attractive. If you have your health, family/friends, are smart, have your job and finances in order, all while maintaining an active social life you will be extremely attractive to suitors.
Now, once you have the infrastructure in place, if a guy asks you out and you are free, go on the date. If you are not free, but are interested, say, "Thank you so much for asking me out. I would absolutely love to go. Unfortunately, I have plans. But, I am free next Tuesday or Thursday at 8PM if either of those work for you?"
Key Points: If you reject a man's initial date, you must offer SPECIFIC times to make the date happen. Men are not mind readers and if you reject the first date they may think you are not interested. If you are not interested, they move to a girl that is.
In order to drive home the point, dating shouldn't be about games (pretending to busy). It is about building a great life for yourself, attempting to find someone worthy to share it with, and finally effectively communicating with suitors so they constantly and consistently know where they stand.