The answer:

It is almost impossible to hunt; the only method seems to be to take advantage of the unicorn's great love of purity and innocence. If a young virgin is placed in the unicorn's way it will approach with reverence, lie down beside her, lay its head down in her lap, and fall asleep. The hunters can then capture the beast.

Or: To catch a unicorn, a beautiful, young woman must sit beneath a tree in the woods and sing softly, if there is a unicorn present, the it will come and rest it's head in the woman's lap, and then the woman must place a golden bridle on the unicorns head. There are also stories that if a young virgin offers to nurse a unicorn it will then gladly follow her and do as she wishes.

May be useful, My English teacher told me this one so excuse language. First find your unicorn, best if it is quietly eating or something then stand in front of a big tree and shout 'Oi D!ck Head come get me' as unicorns are proud beasts this will make it angry and it will charge you, at the last second step out of the way and it will get it's horn stuck in the tree, limitedly use excessive chloroform to put it to sleep and there you go the perfect unicorn.