One of my favorite ways to teach attitude is to have the students, for example, take sur le cou de pied front, and holding that shape/position, simply lift the leg to the front. Hold it there, then lower to tendu front (holding it there too) and then closing into fifth.
You can do the same from passé/retiré; extending the leg out front, be carefull to lead with the heel, holding and then lowering to tendu and closing.
In terms of directions for these positions and for dévelopée, I usually like to do front first, back second, and a la seconde last as it's the hardest position to "get."
For arabesque position, I always have the students (Ballet I) begin by facing the barre (two hands on it) and beginning with tendu back, lift the leg, being careful to hold it stretched, coming back to tendu, and then closing and holding fifth, making sure everything is straight and placed.
Common faults tend to be distorting positions, alignment, and placement as they move. The challenges are learning, feeling, and remembering (aka, reproducing consistently) what may move and what needs to stay. How to move, make positions, yet keep true to form. Keeping legs and knees stretched, weight over the ball of the foot, shoulders relaxed.
For all students, but particularly beginning ones, I work with them one-on-one a lot, so they can get some help with all of the above! More experienced students usually just need a gentle "reminder" -- the touch of a finger on a leg that's not fully stretched or under a droopy elbow.