What is the "best practice" on taking down a helicopter with a (single) Stinger?

Solution 1:

Works only on some pilots, but here is the method I use:

Firstly, I get a lock onto him and wait for him to lose his nerves and fire a salvo of IR-flares.

Then I fire my first missile, and immediately after that the second, if he is still in sight and range.

This will consequently fail on experienced pilots, since their first reaction is to fly far away if they can, and if not, they wait for the threat missile launch, and then release the countermeasures.