Beginners are often confused by contra dances in which they focus on their partner across the set and progress sideways. For a first contra, I recommend that you start with a dance where the progression is "Pass through to the next" or "Duck through to the next couple", so that the dancers are focusing their attention up and down the set. In fact, you can start by having them do a Sicilian Circle, then stop, change the sets into lines, and have them continue with the same dance. Haste to the Wedding is a good choice, or here's a dance of mine which has been successful with beginners.
Jacob's Polka Contra by Jacob Bloom
Duple Improper
Music: polka or polka-like reel
Requires extra room up and down the line
Give both hands to the next, or take ballroom position
With the outside foot, heel, toe, two slides out, with inside foot heel, toe, two slides in
Heel, toe, two slides out, Heel, toe, two slides in
Dosido below
All dosido partner
Allemande left below,
All swing partner
Circle left with same couple
Pass through, bow to next