Rainboe has it.
Below FL100 do not touch the FMC: besides it only understands 1s and 0s as it is a computer. It doesn't have the nuances a pilot has.
Choose an arbritrary point somewhere along your inbound track as a 4 pane window: the ideal position is on speed, on altitude at the intersection of the horizontal and vertical window bars. If you are in the top left pane, high and fast, you have a problem. If you are in the bottom right pane, low and slow, you have a problem, if you are high and slow or low and fast, you have ENERGY that you can convert.
Think Groundspeed: divide GS by 2 and multiply by 10 or if you can just multiply by 5 for the ideal ROD. If you are doing 400kts GS you will need 200fpm to maintain the 3 degree slope. Reduce that to 150kts and the required ROD changes to 750fpm.
Think wind. What will happen to my GS and hence ROD when I turn base, establish on final etc.