A step by step guide to help you master this step by Artistic Associate of The Qld Ballet Robyn White.

Saut de basque is a difficult step to execute correctly.
There is a preparatory exercise which I find very helpful.
 Here it is, with the counts underneath:

‘and’  Demi-plié in 5th éffacé (ouvert), weight well
centred on two legs. 

‘a’ Extend the leg devant, weight still firmly on
the back leg.  Make sure that your shoulders stay back over the toes of the back leg, don’t let them come forward and drag your weight off the back leg.

‘1’ Step forward into plié on the front leg, keeping
the back leg straight and making sure that your hips are straight and not tilting back.

‘and’ Now swish your back foot through 1st position,
still in plié, hips absolutely straight over the toes and not tilted back, into…

‘2’ …A strong battement into 2nd position at 90˚
on demi-pointe with a quarter turn to face the right, back corner.

‘3’ Forcefully close the battement leg to
reach 5th position on demi-pointe (sousous).  I say ‘forcefully’ because when you jump your saut de basque, the action of this leg coming down helps the jump to go higher.  Your arms and head are now positioned as they would be for the first quarter turn of a pirouette. 

‘and’  Now turn a half turn to the right, finishing
croisé, turning into the right arm which now places itself into 3rd position, and your head is en face.

‘4’ Lift the right foot sur le cou de pied devant and
plié on the left foot.  Now you are ready to swivel into the éffacé (ouvert) position to begin the whole exercise again.