How to effectively practice violin
The secret to practicing an instrument is not how many times you practice the same exercise over and over. The secret is in playing the same thing over and over again, but in different ways and with different methods.
For example, if you are going to practice Mary had a little lamb effectively, first analyse the piece of music. Look at the time signature, Look at any ornaments, volume indications and other symbols etc. Then play it through on the violin once.
The second time, practice it with counting out loud as you as you play the piece on the violin. The third time, play it in perhaps playing each note four times. Make sure you practice it in different ways, at least three different ways.
The key to how to effectively practice the violin is in variation in your playing through of the music.
Another important thing to do is in any piece of the music that you are struggling with, play just that one piece, that one bar or one line slower and over and over again until you get it right. then add it into the rest of the piece again. This is how you effectively practice the violin.