What helps me the most is giving a model tighter rules instead of just saying "make this look good." Rules like what should be the main element on the page, which things shouldn't compete with it, examples of the vibe I want, and especially what I DON'T want. Then I look at what the model actually made and react to that.

Using multiple models to help test different directions/takes on designs is also an approach I utilize. I'll even have models critique each other's designs and suggest improvements sometimes too. Depends on how difficult it is for me to decide on a direction I want to go in.