How do I break a bad riding habbit?

I know how you feel with going from western to english. I am an ex barrel racer and pole bender but now I can only ride horses occasionally at a boarding/instrution barn since my horse died from cancer eight months ago. If you start making yourself have good posture all the time you need won't need to slouch when you stop. The rein problem can be fixed by not letting go of the riens, just let out some slack in them so you can scratch your horses neck and play with it's mane without disturbing it. But ultimately you do have to think about what you do.