It sounds odd, but one of the most entertaining things I do with Photoshop is to improvise on a theme. That theme can be a compositional style, an effect, a genre, etc. Part of this experimentation relies on anchoring around some idea or look. For example, I recently posted a challenge on PhotoshopTechniques to come up with different ways to use noise in an image. Most folks use noise to simulate film grain, and this is where I started. The specific challenge was to get noise to behave in unusual ways.
Since I like to have the image do much of the work itself, I try to build effects that rely on color or brightness information. This allows for some custom looks, but also helps when building film simulations since much of the look of film is tied to how it handles tonal variations and exposure. Noise in film is actually grains of photosensitive material, with grain size being related to the sensitivity of the film.
Without getting into the technical details, here’s the summary of film, and why it’s important to this discussion… Color film is made up of layers, each sensitive to a different spectrum of light. Sometimes these layers react differently, or have different sensitivity to various frequencies of light. Noise in these layers comes from "improper" exposure, typically underexposure. So, to get good (or realistic) simulations of film grain, you have to apply noise in a way that mimics how the film reacts to being underexposed.
The best way to do this is to use channel information and blending modes. There are several approaches, some requiring more finesse than others. Here some things to try: create various noise layers and adjust the color with hue/saturation, then apply different blend modes and opacity changes; add noise to special selections, like highlights or mid tones; warp your noise layers using displacement maps created from edge masks.
These are fairly advanced techniques, so if you are not sure how to get started, check the links on the right and send me a question!