Here are some of the key areas:
1)Timbres - using interesting timbres within an ensemble. For example, pizzicato on the violin
2)Textures - what different tectures can you achieve within the ensemble? For example, homophony, polyphony and canon
3)Harmony - don't be stagnant. Move to another key within your composition
4)Melody - Create a motif and develop it through techniques such as: sequence, fragmenting, transposing, inverting and passing it through different instruments