Practice this variation at first with a slurred bowing on the string, to work on your bow division and smoothness of string crossings. Use a round bow for the string crossing with the upper arm moving smoothly to the next string. Start the string crossing action right at the beginning of the slur so you do not need a sudden jerk to get the bow over to the next string.
The first part of the variation is in the lower half of the bow so use the side of the hair for a clearer sound. When you add the lift or brushstroke to the slurs, using the side of the hair makes it easier to keep the bow close to the string.
Be mindful also of the phrasing of each bar, that is the first beat and beginning of the slur is strong and the third beat (even though it is right at the frog of the bow) should not be over-emphasised.
Practice the lifted stroke firstly as a standing spiccato on one note before combining it with the slur. The standing spiccato stroke can use some movement of the forearm, fingers and hand, but also requires a passive reaction in the upper arm.
For the left hand use the harmonics in bars 9 and 10 to make sure that the left hand is peacefully back in 1st position before the bow articulates the beginning of the next bar.
Observe Ševčík’s markings for where to play in the bow, in the lower half for the louder dynamic and the middle for pp. It is effective to finish with a very soft final chord.