Alright, go to the RNG Time Finder. There you go to the tab 4th/5th Gen Shiny Egg. Select BW, min frame 70 max frame 200 and a month. If you don't want it shiny, leave the ID and SID box empty. Then, select nature, ability and gender and get the right gender ratio.
Then, if you are breeding with a Ditto, check that 'Ditto Parent' box on the left side. If not, keep it open. Now you are going to enter the parent IV's. (below the Gender Ratio)
On the right, you can fill in the IV's you want to have. If you have parents with the right IV's, for example: If they both have 31/30/30/31/31/31 and you want those IV's on your baby, you can enter 31/30/30/31/31/31 in the most right section of the Time Finder If the parents have a few IV's correct, then you could search for >=30 in the wanted stats.
Don't forget to put the KeyPressCombo to 3 (5th Gen DS Parameter Setup) and then hit Generate. :)