It all boils down to how well you know your own vehicle and the speed range limits in each gear, especially 1st gear.
Once engaged in 1st gear many vehicles allow you to slow down to idle, about 6 kph in most cars, and will not stall if you release the gas. Some BMW’s idle as slowly as 4 kph, whereas others let you slow down to no less than 10 kph.
When driving in 1st gear above idle you simply play with the accelerator while staying off the brake or the clutch.
Below idle speed hold the engine RPM slightly above idle with the accelerator and control vehicle speed with the clutch pedal.