I was never really sure whether the two kribs i picked up had already been an established breeding pair, got the female from the local lfs and i was in the next day getting some bits and bobs and suddenly realised that there had also been a mature male in the same tank (must have been hiding

)
But within a month i had my first batch of fry and a few months on they are looking great, although i should have got them off to better homes before now but should have them re-homed by tuesday.
You can always tell when mine are getting ready as the female's belly becomes especially red and dark purple, and she will hover slowly around the male with her body arched so that her belly is stuck out toward him. Then she disappears into their preferred cave for about a week and next thing i know she will appear leading a little troop of fry around the tank =)
I have read and been told that Kribs are not the fussiest fish when it comes to pairing up and that the intensness of the female's belly only becomes important within groups (the male usually choosing the female with the reddest belly) so assuming that they are both sexually mature already and as long as the female can work out how to get his mojo working ^^ u shouldnt have long to wait
And a word of warning; apparently kribs often take one or two hatchings before they learn how to get things 'just right' for the fry so if the first batch or two dont make it (another reason i think mine may have been an established pair) i wouldnt beat urself up about it and rack ur brains trying to work out if some of the tank conditions are to blame but would just wait and let them have another go at it.
gl and hope u r the proud breeder of some baby kribs soon
EDIT: (in case kill a wat checks back) is ur tank heavily planted? I found out from a well written source that kribs prefer heavily planted tanks so long as u leave a space for swimming and mine did seem to love the addition of new plants to my tank (spent hours watching them zip in and out of stalks and leaves), so u might want to find a way to break up ur tank so that they cannot constantly see each other if u havnt already. My male loves to chase the female too but so long as i provide more than one cave and they cant see each other all the time then all is good.