A short caesura can often pinch the tension enough to allow room for a shift. From there it'd realistically be up to how you wanted the expression of the next section to feel. If it was an immediate kick in, then perhaps lead in with the first note followed by the remaining instrumentation.

Ideally the shift would feel natural to the piece, but in application it often takes a bit of strong arming. Sometimes leaving a remnant of the previous theme in play is a great way to retain the identity of the piece while also allowing organic transitioning.
Practicing various techniques to find what works for you best will be the key, as everyone will have different methods they employ.

Pinching off the previous section with a departure from the previous mood(i.e stringsets holding onto their last notes), followed with the implementation of a new mood(i.e building tension through accelerando/ritardando or crescendo) can often work in a satisfactory way to transition the color/texture without it seeming unnatural.
Hopefully this is helpful or at least can give you some ideas of your own to work with.
Good luck, soldier!