How to lace a corset
If you want to lace a corset please follow the scheme below. In my eyes, it doesn't matter whether you lace criss-cross or the way they did it in the picture (maybe tightening the laces is easier this way, but criss-cross looks nicer). It also is not that important how you close the laces (either by connecting them at the lowest pair of eyelets or making two knots keeping the laces from slipping through said eyelets). But you should take care to have two loops of lace in the middle eyelets i.e. where your waist is the smallest/ the waist of the corset is. It's not suitable to pull all the excess lace to either the upper or the lower corset hem, in the style shown below it is easier to equally distribute the lace and the pressure while lacing!
When tightening the laces in your corset, you should move the excess of laces to the middle loops. If someone else is lacing you, you can help them by holding those two loops tight and readjusting them while you are laced. If you are alone, don't fear: I find it easiest to hook both loops on a door handle and walk away from the door while lacing myself, thus keeping the loops tight. In the end you should make a tight knot with the two loops and think about the excess laces. You can either hide them by pushing them under the side of the corset (though this might be uncomfortable), make some more knots to keep them from tangling into your legs or make a nice bow. Unless you want to make a fool out of yourself, please refrain from pulling them to the front and lacing them there! This will cause strain on the back of the corset and may damage your outer fabric is the laces shrub against it when the corset adapts to your body!
Common fitting mistakes
Now that you learned how to lace your corset properly, let's discuss common fitting errors. Beware that many sellers (i.e. Hot Topic or Xtra-X) who don't specialise in corsets also have very little knowledge about corset fitting. Of course you might find a corset lover and fitting guru there as well, but this is rather an exception than the rule... You should also keep in mind that these people want to sell you something and might tell you that "the fit isn't that bad" or "the pain will go away after the corset is worn in". This is absolutely wrong. A corset should never cause you pain!
After this little rant, let's check how a corset should fit in the back:
This corset has the opposite problem: It doesn't fit at the hips. Since it is too wide at the hips, the pressure from lacing will be increased at your stomach and chest. This might bruise your ribs and cause serious discomfort. Please don't buy ill fitting corsets!
If you experience this fit on several corsets, it might mean that you yourself are more asymmetrical than average Joe. Most people are slightly asymmetrical (my left side is a little longer), but this can lead to back pains or even headaches. I recommend getting checked up at a doctor's in case you didn't know about this issue before. While a corset can help with asymmetry and back problems, I advise you to only buy custom made corsets from a maker who knows about your issues and offers fitting sessions.