During descent, keep the map updated to give as 'true' a track miles to go as possible and use PROGRESS page to monitor height/mileage. Keep a mental cross-check going of the VNAV profile; ie. passing 25000'(FL250) drop the zeros and multiply by 3, ie 25x3=75. That gives you a requirement for 75nm to achieve a 3 degree slope, then allow for speed reduction; 1nm for every 10kts to lose. Some people just do 3xheight+10 which also 'get's you in the ballpark'. What you are trying to achieve is thrust levers closed at TOD and only spooling up on finals.
Have fun, it's a top piece of kit!
PP