Rule of Thumb
On the 737, you can figure a descent profile at 250 KIAS of about 3:1. That is, it will take three miles to descend 1000 feet. (This assumes clean configuration, idle thrust.)
If you have a bit of tailwind, figure the 3:1, but add a mile or two for the tailwind.. For example, you're at 10,000 feet and 250 KIAS, maybe 25 knot tailwind throughout the descent, and you're cleared to descend to say, for example, 4000 feet. That's 6000 feet of descent...at a 3:1 profile...that's 18 NM. Adding maybe three or four miles for the tailwind, gives you 23 or 24 NM to do this level change from 10,000 feet to 4000 feet.
Note: If you're above 10,000 feet (What I'm saying is, you're not restricted to the 250 KIAS speed limit.)...descending at say, maybe, 300 KIAS...figure a 2.5:1 profile. So, descending from FL 350 to 10,000 feet is a level change of 25,000 feet. Idle descent, no speedbrake...no wind...figure 2.5 X 25 = 62.5 NM. Really, just round it up to 65 NM...it'll be more than OK. Now, add 50 kts of tailwind in this descent example, and I'd add at least 10 more miles...try, say, 75 miles for this example.
The old rule of allowing one mile for each ten knots of deceleration is pretty good. And, I really don't think it makes THAT much difference if you drive down to 10,000 feet at 300 KIAS, do an abrupt pull-up to level at 10,000 to slow to 250, then continue the descent...OR....do a gradual deceleration while you descend...say, for example, start easing the nose up at 12,000 feet, timing it so you're at 250 KIAS as you descend through 10,000....I really don't think either way makes much difference in your descent profile. (I vote for the smooth method...but whatever works for you, works for me....)
The old rule of being at 10,000 feet AGL, 250 KIAS, 30 NM from the airport is also a good one. I used to figure...if I have to go past the airport to turn around and land the opposite direction....10,000 feet, 250 KIAS, 25 NM out is good. OR, the other extreme...landing straight in...be at 10,000 feet, 250 KIAS at 35 miles out. If you'll be entering a base leg to land...then, the 30 out at ten and 250 is great. Again, add or subtract a mile or two for wind.
If you're off in your descent planning, you won't be off much. Too low, add a small bit of thrust. A bit too high, speed brake for a few seconds will make the needed correction. One common error is for pilots to use flaps/slats as a speed brake. I suggest you use the flaps/slats at the scheduled speeds that your company's SOPs dictate. If you're REAL high, speed brake and/or gear will most times give you the drag you need to get back on the desired profile.
While your company's SOPs are more important than any other publication, most operators use the 1000 feet AGL to be stabilized in IMC conditions or 500 feet AGL in VMC conditions. The idea is to plan your descent to acheive these restrictions. The closer you come to doing an idle descent from cruise altitude...to easing up the thrust to be stable at 1000 feet....well, that's quieter, more fuel efficient, easier on the plane, easier on the passengers, forces you to be more aware of a descent profile that gives you adequate terrain clearance, etc.....
If you really want to get fancy...plan on the last 1000 feet of descent at 500 feet per minute....allowing that extra distance to do this. AT 250 KIAS, figure 270 Kts ground speed....that's 4.5 miles a minute...500 FPM descent requires two minutes to descend 1000 feet....so add 9 miles to do this. I'd round it up to an even ten miles extra in your descent planning to accomplish this....you're good to go.
So, you're descending from 9000 feet to 5000 feet (250KIAS, idle, clean, no wind)....from 9000 feet to 6000 feet is a level change of 3000 feet. Figuring the 3:1 profile gives you 9 miles. (I'd round it off to ten miles...just for ease of figuring.) Then, for the last 1000 feet of descent (from 6000 feet to 5000 feet)...at 500 FPM...add another ten miles. So, if you're able, allow 20 miles for that 4000 feet of descent.
Anyway, have fun with the 737. It's a great airplane. It simply requires a little more descent planning than other planes. But, it's a great glider!
Fly safe,
PantLoad