Answer:
The easiest way is to use a depilatory preparation such as "Veet (TM) for facial hair"
The most effective way, especially for ladies who are blessed with strong, dark facial hair, is to employ electrolysis. However this takes a while, can be expensive and may cause some temporary irritation. The good news is that it is usually permanent, which makes it an appealing option in such cases.
Do not wax, shave or pluck the hair, this can be excruciatingly painful and will only encourage a thicker regrowth. A cosmetic bleaching and dissolving agent is preferable; but electrolysis is the best.