Practice everything equally 15 mins on each (thinking about the following: right hand, left hand, pizz, arco... etc... Its longer but you'll progress faster.
I.M.O... Its what I would teach to a student!
Use some sticky rosin, Kolstein all weather or pops (might be too sticky) and play long notes... Open D relax hand, relax arm then you notice big sound
Take your time and you'll be fine
Focus on only open strings for now... You are not expected to play any lines you normally would play with your right hand, so... do what is expected of you... Open strings full bow.. From Frog to tip...
Anyways... I have Some Vivaldi Cello sonata's to attack... Enjoy... Keep at it