W/T/C working balanced and through from behind [headset unimportant as it doesn't really matter where a jumper's head is though headset usually follows correct basics anyway]
Basic laterals [leg yield at least, half pass if possible, travers/renvers also very helpful as with shoulder in]
Shortening and lengthening of stride WITHOUT losing rhythm/impulsion or going flat [extension/collection best but shortening/lengthening is acceptable]
Walk to canter and canter to walk
Canter pirouettes can be a HUGE help in the jumpoff but not necessary, just useful [bearing in mind they won't be good ones and will still have some forward movement not just the lateral because a true correct pirouette is simply TOO collected to use when jumping - but will be of HUGE help with extremely tight lines, and it's the shortest LINE, not the fastest SPEED, that wins...]
Once the horse has those things well and truly established on the flat [with the use of cavalletti and small fences to help establish them] then usually the jumping part comes naturally. It's my belief that every dressage horse SHOULD be able to go out and jump a course at an intermediate height [say 3' or thereabouts] with no special preparation, and every jumping horse SHOULD be able to perform an acceptable dressage test at first to second level [which I think translates to novice and elementary, but I'm not sure].
My boy does everything except the laterals... and flying changes but I'm pretty sure that's more me than him because if I set up a 4 stride line and don't ride dead straight he'll do one-time tempi changes between the fences!
Yes in theory laterals should be easier in trot and canter [definitely easier on the horse!], but my lower leg is not all that strong and in the trot especially I really struggle to get a good leg aid onto him if he wants to ignore my light aids. My dressage saddle is not helpful in that aspect either, very difficult to get leg on in it in the trot and canter, but I am definitely a big part of the problem.
Edit; jumping is just dressage with speed bumps, after all :P