You'll go far, little girl.
Now try hard and be the best
The best in all the world.
You can create a demand
For this your special skill.
You will be healing the ill.
It's surgery, but with no knife.
She'll make a great LeechWife.
To suck out what is bad.
'Cause this is science not luck.
Luck is not what you've had.
But now you've brought yourself up.
Surprise your Mom and Dad
With this, your special skill.
You will be improving your life.
She'll make a great LeechWife
Good sense is what it makes.
You'll learn it in no time flat.
One leech is all it takes.
It sucks the blood till it's fat.
It's found in ponds and lakes.
The dried up skin then turns black.
You can be one of the fakes
The quacks and the riff-raff.
She's honing her LeechCraft.
Leech empty, leech filled.
She's honing her LeechCraft skills.
Just think of the folks that she will heal.
She'll make a great LeechWife.

This is about a young girl learning a "special skill" for using medicinal leeches to suck the blood to heal patients. It's almost like an advertisement from older LeechWifes that are looking for some people to teach their skill to, giving the reasons why becoming a LeechWife would be good (You can create a demand For this your special skill.), and how easy it is. Its depressing that back then they didn't know any better and if this technique did save any patients it was pure luck even though they thought it was a good healing method.

Melora said somewhere it was about the lords wives, in the middle age, who tempered their husband's angers, and saved people making the lord be kind.

But leeches are still used today, and they DO help people. And that's not luck.

ninja monkee,
it is true that leeches are still used today, but in a much different application
in the medieval era, people believed that the body was balance by 4 humors or tempers, each with its own associated body fluid: sanguine (blood), Choleric (yellow bile), Phlegmatic (Phlegm), and Melancholy (Black bile)
leeches before were used balance a person's "humors" when they went out of whack, specifically sanguine.
Anyone with reddish skin was given leeches, because it obviously meant they had too much blood, and if their behaviour was too loud and wild they were considered to have a "sanguine" personality, and once again, were given leeches to balance it out
so while they are used today to reduce swelling and junk, they weren't really used efficiently back then
that said, a leechwife was, in theory, a nurse who applied these leeches, though i'm not sure they actually existed as the song suggests, considering most women did not go into the medical field until after Florence Nightingale.

I think it has two meanings, of course what Vamped Vixen said but also a gold-digger type, "study hard and go west" she knows what to do and is heading to new territory where the men don't know her tricks
"You get those suckers to suck To suck out what is bad. 'Cause this is science not luck. Luck is not what you've had. But now you've brought yourself up" She has her process all thought out.. the leech part is that she becomes very attached to a guy then sucks out his money in a way.