another useful exercise is to take a 32bar jig,and try reversing bellows every bar,then try it every two bars,and see which you prefer.
one thing i notice that I do,is include lead in notes to phrases in the same direction as the first note of the bar[something that I notice a lot of irish fiddlers do].
most jigs have the strongest emphasis on the first beat of the bar,so changing direction every bar,although perhaps predictable,isnt going to be distracting from the dancey feel of the jig.
I think that I tend to change direction every two bars,and ocasionally,one or three bars,or even four bars.
its even worth experimenting,with changing occasionally twice in a bar ,on the first and fourth beats.
but the most important thing with jigs [in my opinion] is to get leadin notes to phrases ,the same direction,as the first note of the bar.