Best end of print procedure?

[BasKoning]

Hi. I am a total newb, with a Creality Ender 3.

Most prints go fairly ok, but at the start I always have some trouble:
after heating up, I start the pint, the nozzle then starts ejecting a very thin string of PLA about 10 to 20 cm long.
Then the machine starts beeping, displays: 'change filament'.
I then press the knob, and it continues to print just fine (after a few circles of printing 'nothing')

Perhaps the PLA inside the nozzle is giving problems at startup?
What would be the proper procedure when the print ends?

Leave the PLA in, cool it down quickly? Or pull it out, let the nozzle drip empty? Or...

[Roberts_Clif]

This first part is telling you the filament run-out sensor is not detecting the filament.
Does the Ender 3 have a filament run-out sensor?

Then the machine starts beeping, displays: 'change filament'.
I then press the knob, and it continues to print just fine (after a few circles of printing 'nothing')

I normally print a 2 line shell to get the filament flowing smoothly before the print begins.

Perhaps the PLA inside the nozzle is giving problems at startup?