First up you'd normally be at 3000 feet at 10nm not 20nm.
As to your question, provided everything remained the same, that is gear/flap/slat settings and speed remained the same then nose must be pitched down relative to where it is for level flight in order to commence a descent. That is basically done with the elevators. Elevator trim is a secondary function that keeps the nose where you put it. Lift dumpers/spoilers are not the primary means of descending and would normally only be used to help slow down or to fix a situation where you are too high.
Disclaimer: Not a 737 pilot, but this stuff is the same for nearly everything.
Further info if you can follow it. Flaps and slats change the effective angle of incidence of the wing (the angle between the wing and the longitudinal line of the fuselage.) Flaps increase it and slats decrease it. Having more flap extended will give a lower nose attitude for a given speed and flight path, extending slats will give a higher nose attitude. For every change you make to flaps and slats you need to adapt to a different nose attitude.
Last edited by AerocatS2A; 20th May 2012 at 09:28.