The main tip to get better at creating realistic mock-ups is to listen! Listen to as much orchestral music as possible. Especially from the masters. Listen to impressionist orchestral music like Ravel and Debussy. Arnold Bax and Delius. Closely hear how all the colors of the orchestra are playing and bouncing off each other. The levels of each section and individual instruments.
When you get a good ear with orchestral music, writing mock-ups become infinitely easier. You can quickly tell when a line is slightly off and how to fix it.
I hear many midi created music, with such wonderful compositions, but the virtual instruments just seem....off. An orchestra is an organism with different parts and sections. They all work together seamlessly. Listen closely to it and try to recreate it as best you can.
As this is my first daily post for tips on composing (and more importantly, in regards to fantasy music), I wanted to relay a suggestion I received when I was starting out.
It is called the Rule of Threes. Basically, with orchestral writing, you want no more than three primary things happening. When you add a fourth, it gets too difficult to follow with your listeners.
Let me give you an example. When writing a soaring adventure piece, here are three components you might use: Some great staccato strings or runs in the background, a grand melody/theme by the french horns and trumpets, then a lower harmony by trombones, tuba, and bass.
Another example. When writing a romantic piece, you can have the strings playing a romantic melody, the horns playing a counter melody, and the harmony playing on the low end to give it depth and color.
Those all have three main components. If you add a strong fourth component, it gets too complicated to focus and listen to. Of course, there a...