Rough Coats and broken coats require hand stripping... Try not to use a stripping knife to much as it can take undercoat as well if used incorrectly, although it is definitely easier on the hands and quicker! . Avoid using a marrs comb to often as again can take undercoat. Jacks have double coats so you must maintain the undercoat. Use a stripping knife on legs and on the knees of front legs, tidy up with thinning scissors. trim around feet with normal scissors and long hairs between toes, keeps the pad close and tidy.
remove long hairs from the ears, define the stop on the head use fingers. use thinning scissors to define any other area's, ie neck, bum behind, sternum, underbelly and any other areas. Don't forget the flag on tail must be removed and tail neatened.
I use thinning scissors as I find they leave the neatness finish and avoids cut marks. The best way to get a jack looking in show condition is to do a bit each one to two weeks in order to keep 'turning' the coat.
also don't forget jacks are meant to be in Natural Coat, so a rough is not meant to look like a broken and a broken is not meant to look like a smooth.
And RuralPug is correct, you don't want your jack looking like a fox terrier..avoid looking at usa groomed jacks as they use a different technique to us in Au.
hope this has helped a bit :)