It helps to look at some object directly downhill. Aim your fanny uphill. This requires more twisting at the waist in the telemark than in the parallel position, because the downhill ski is ahead at the end of the turn. In the telemark particularly, keep pressure on the big toe of the front foot and the little toe of the rear foot to edge the skis correctly while turning. Use the Ski Tests for Practice - If you keep repeating the exercises in the ski tests, you will be working on fundamentals.
Instructors can suggest other exercises.
Any equipment will do. Make a number of turns down the fall line on easy terrain with the same ski always ahead. Notice that you have to unweight to make the turns. Now switch the lead ski between turns. Practice with each ski ahead until it doesn't seem to matter which way you do it.