Your designers are going to do their best to follow your instructions as closely as possible. This means, the more detailed you can be with your request, the better chance of getting a result you like.
 
With that said, sometimes you may ask for a more open ended request, at which point the designer will have much more creative freedom to produce what they want. In situations like this, you can request them come up with a couple different style designs to get a range of ideas. From there, you can pick the direction you find most appealing.
 
Some language you can use when making requests like this could include:

• Can you please try a few different styles for this request? I’m not sure the exact direction I want to go yet.
• Use your creativity on this one!
• Let’s apply some new design trends to this project. Use your creativity!