Practice together as much as possible. Help each other stay on top on your own pain points. Take turns singing and playing. Record your playing to sing to if necessary to separate playing and singing.
Make sure your effort is high and channeled in the correct ways to progress. Volume and physicality should be paramount.
Minimize thinking everywhere possible. Use it only for problem solving when necessary.
Keep your eyes on your left hand always. Break habits of looking at right hand and don’t look around while executing.
Be discliplined with your form and function. Make sure things feel and look right.
Double and triple check posture throughout practices.
Hold uke on leg right, arm on uke right, neck in channel of palm, etc.
Progress to singing and playing at the same time after getting each down separately.