Planning Movements

I'm in the process of writing a piece in sonata form, but I feel that I don't really know how to plan the music so that it is coherent. Could someone go through their process when it comes to planning.

I mainly want to know how detailed you make plans, and if you come up with themes before or after, and what I should be doing regarding tonality structures. 

And also, do you have any tips for making interesting accompaniments for orchestral pieces? I want to move away from block chords and into something more like the orchestration of Dvorak's 9th. I use that as an example because it's something I've been listening to a lot recently.

Thank you for your help!

I think I can help you kill two birds with one stone here. 

When I start a piece I like to make a graph of what I want to go on. It can have a few musical notes here and there, a theme if the piece has one, and other things like chord progressions or set classes that I want to use. In my graph I might add adjectives to describe what I want, they don't have to make sense to other people because they are your notes.

In the graph I want to show major changes like for example:

| A section: fast, whirling woodwinds (might have a squiggly line going up and down showing how I want the woodwinds to move), Minimalist brass on F Major seventh chord and B minor Seventh, melody in the Strings in octaves|

| B Section: suddenly slower, low strings feature, cluster chords in brass, darker, undulating woodwinds (might write out a variation of a theme from the a section and write what instrument gets it)|

|C section: development, crunchy, harsh, slowly gain speed|

|A section prime: brighter, more whirling,|| D section: introduced in low strings underneath A prime|

|Finale: chaos but still optimistic, big fat final chord, percussion continues|

that is just one way I might sketch out an idea. In my sketch I also plan out the accompaniment too. Keep in mind, your melody doesnt just have to be in one voice all the time, create dialog between instruments and sections. Also countermelodies are great, bass movement, complex and interesting ostinatos, ornamented sweeps and runs above the melody, and a variety of various things can keep you from doing just block chord accompaniments-- all of what can be mapped out in the sketch. Their is no right or wrong way to do a sketch, just as long as it gives you a roadmap to where you want to go. 

Thank you very much. I think I get what you're saying. I'll try my best to take it on board and improve!