The orchestral music begins with writing good arrangement, you can do this on paper or record it using piano. Once you have this sketch, you must know a lot about orchestration so you are able to put right voices to right instruments. If you dont know how to compose, arrange and orchestrate, it doesnt matter if you have all articulations and best of the best sound banks - you simply dont know what to do [:S] So listen to music a lot of orchestral music, study orchestral scores, practice harmony.....etc. etc.
If you know enough about theory and you have practice in writing music {not sequencing} your workflow should be easy. After I record musical phrases I am listening to those phrases and record all controllers I want {xfade, expression, etc.} sometimes one by one sometimes simoutaneously two or more at once {sure you need fader controler with more than one fader for this}. Keyswitches are made in realitme and sometimes by entering. As you can see there is no tutorial for this, because every instrumentation every phrase needs different approach.
But firstly you must have clear idea of sound in your mind and then you just reproduce it into sequencer. VSL and other banks are not holy grails, you must have extraordinary musical knowledge to create extraordinary compositons. VSL is just simply best orchestral tool to accomplish your musical ideas in orchestration world.
One good advice that helped me - try to recreate some scores that wrote masters {Beethoven, Brahms, Prokofiev, Ravel, etc. etc.} You will be surprised what you can learn from it....
thats my toughts....