Introduce some random
It’s easy for our ears to be drawn to the same kinds of sounds each time we work. One way to get past this is to try plugins which allow you to experiment with randomness. NI’s Absynth 5 is a good example, as is Synplant. By choosing how far from the currently loaded sound you want to ‘travel’, you can either reinvent the sonic wheel, or experiment with subtle variants. Omnisphere 2 has an interesting approach to this too; choose a sound and then ‘lock’ particular parts of the engine before selecting parameters from a second sound, producing weird hybrid tones in the process.