The salivary glands are just dull gray sacs. Use a dissecting needle to move the glands away from the carcass. Adding small drops of Ringer s solution may make it easier to move things on the slide. Remove the carcass and try to clean off large bits of fat from the glands. Try several dissections.
Some larva are more accommodating than others, and practice helps.
Do not let the glands dry out at any time or the cells will burst. Leave the stain on for 10 minutes for it to penetrate. Add more stain if the slide begins to dry out at any time. After 10 minutes, wick away any excess stain using a tissue, then place a cover slip on top of the stained glands. Place a folded paper towel over the slide.