Playing a musical instrument involves complex coordination, so tension is inevitable. Body scan is essential before, during and after practice. It may take some time to get used to body scan in the beginning, but I guarantee the process gets quicker and more intuitive the more we do it.
Tension is most commonly shown in the following places, and so these are things I always check for:
It really helps to scan through the entire body especially when we are practising something difficult and check different parts of the body one at a time. Tensing up muscles then releasing them also helps if we are not sure whether we are still holding any tension. Being tension free not only prevents injury, but it also makes playing the instrument easier. Sometimes technical issues are solved just like that.