"Before practising your mixed rhythms, make sure your left hand is comfortable. Practise with slurs at half tempo. When you begin practising mixed rhythms make sure you use a small enough amount of bow and enough bow friction. Turn it around. Try it in fours. And turn that around too."
Practising with mixed rhythms is one of the most important ways to improve accuracy and clarity in passagework.
When practising in rhythms make sure that:
The dotted rhythm is crisp enough to challenge your coordination (the short note should be very short).
In the break you prepare the next finger (and the string crossing if there is one).
You maintain a clear firm sound and do not use too much bow.
In the practice breaks, analyse your performance of the notes you just played, repeat the group if necessary and plan and prepare the next group of notes.
Scores - Mixed Rhythms - violin & viola