There is good advice above but... if you do that without dropping your weight by bending your knees you will get pulled over and lose confidence. It's a balancing act - the more you can drop your weight low and balanced over well anchored feet, the more you can handle the power of the rig as you sheet in and move the mast forward, which will lead to better board engagement. I'm no expert but I have learnt this the hard way - when I'm tired at the end of a good session I'm far more likely to either not bend the knees or not sheet in enough and push forward.
It's the same in the foot transition, if you can't balance on one leg (you need to bend your knee for that), you are not going to have a balanced foot transition. Get your weight low.
Another tip to remember is - Eyes, feet, body - look where you want to go first, then move your feet keeping your body balanced, then move your body to the new direction. I don't think this is unique to a windsurfing move, watch ballet, martial arts, gymnastics - it's pretty common but for gumbies like me it does not come naturally. I'm more likely to move my body while watching my feet
Look at Peter Hart here - eyes looking out of the turn, front arm extended pushing the rig forward and away, weight really low and body balanced over the feet that are securely in the straps.
Then have a look at a classic karate stance - it's called the Cat Stance, and it's all about being balanced on one leg so the other can 'do stuff'. This is a great one for the foot transition, the knee is very bent and supports nearly the whole body weight on one foot. This allows you to look to the new body direction, move your front foot, then move the rest of the body by keeping the hips moving in the same plane (not rising, just rotating).
Have a look at Jem Hall to see what I mean, knees really bent to balance the sail forces and the power managed through the 'core'
and the Cat Stance for the transition keeping the weight low and eyes looking out of the turn which leads to the correct head and torso position for balance