You don't need to dust the repti worms. They already have an adequate amount of calcium.
When you offer crickets, I suggest keeping them in cardboard tubes for toilet paper or paper towels to make them easy to shake out. I shake them into a cleaned yogurt cup with some supplement (anything similar will work) a few at a time and shake them gently. Then I let them out a few at a time so it's easy for me and my dragon to track them. I repeat this until he loses interest or after about 10 min or so, making sure I remove all remaining bugs after the meal time is over. Leaving bugs in the tank can let them hide and come out and bite your dragon overnight which can be an irritation if a few but if a lot are left they can do some real damage.