ATC will take you down to a certain level, like FL070. Absolutely no planning required.
They will keep you there to a certain point, where they are allowed to let you descend further.
This luxury is only enjoyed in few parts of the world. However it's not an excuse for not knowing your aircraft.
Surprisingly many captains from such countries who join us, have no clue on how determine whether they're on profile or not, unless they have the route accurately programmed and then read the VNAV profile. Situational awareness is key when flying.
You always have to be able to see through the clearances and keep a backup calculation on what the ATC tells you to do. Usually as a captain, you're solely responsible for what you do. I've been cleared to fly into mountains and other airplanes' paths by ATC.
What the original poster is asking about, is how to manage his deceleration / configuration - while continuing to go down.
You reduce the vertical speed to let the airplane decelerate. Very easy, I even did it during my first ever flying lesson.
However, if you want to have a continuous descent and reach a point at a certain altitude, configuration and speed without adding more thrust than necessary, well... then you have to do some planning!