Here's an update ever since then...
- Communication is Key!
- PITCH! - When messaging models have a set and well developed "pitch" message with creative concepts with specific details on everything you have in mind, especially with wardrobe if possible. The more details you have (relevant information) the better for serious (professional/mature) models. This should increase your response from the models. But this would also depend on your portfolio so ensure you have properly selected the photos displayed in your portfolio.
- and be organized!