Making movements fluid is about making them continuous. Since your arms are not infinite the only way to do this is to make the end of all techniques (and more importantly all parts of a technique) circular. So shuto for example doesn't stop in place but gets to the peak of the technique and keeps moving in a gentle arch round and into whatever chamber position begins your next movement. Also preparitory movements should circle in the same way as opposed to thrusting into place as we often see in shotokan classes.
Another thing that you can practice that helps smooth movements is harmonising with your breathing, especially across segments of kata is trying the kata with each whole technique taking up half a breath, i.e. left low block (breath in), oizuki (breath out), turn into right low block (breath in), oizuki (breath out)... etc.
Notice your lungs never stop moving, they expand and then seemlessly fall into a contraction and back out to expansion... forming a sinewave pattern; your movements should do the same through the form.
It's Shotokan not Shoto-can't!!!