Mixing textures is a well know way to make an outfit look distinct. Furs with jeans, velvet with cotton, exc. Layering on things, however, can make someone pretty uncomfortable. Eventually all those extra layers can get sort of warm, and sometime you want to look distinct without looking like you're completely whiling out.
The next best thing is iron-ons. But not regular, matching iron-ons. The best iron-ons are the ones that match enough with the fabric they're being ironed onto to be as distinct as texture layering. Even though you're working on a small scale and with slightly different tools, the mentality is the same. If the two items you're combining are "opposite", while not necessarily clashing, then you've made something distinct.
The best example of this is florals and strips. Florals in real life are made out of petals, which are fairly different then textured striped shirts. Just imagine the iron-on and the shirt as their "rawest" version: petals and fabric!