The first thing you need to do when glaze is being used is to wipe down or wash the piece with clean water. Make sure you remove all the dust and any loose particles. Also, make sure your hands are clean and make sure lotion and any oils from your skin do not come in contact with the piece you are working on. When the piece has been washed the glaze goes on smooth and does not dry as fast leaving a nice finish. Any dust may leave pin holes in the finish.
Always read the label on the bottle of glaze you are using. Some glazes, like underglaze, need to be top coated. Others do not. The number of coats you use make colors solid or transparent. Using a good brush made for glaze helps leave a smooth finish. Never over work the glaze. Put down even coats keeping a wet edge then move on so you don't pull off the glaze you already applied. Let the glaze dry between coats. If the glaze is thick and will not flow well add a few drops of water or mix a brush load of water into the puddle on your pallet. Don't have a pallet use a lid from a plastic container or aluminum foil. That will prevent contaminating the bottle of glaze. It's always helpful to have a container of water or two to clean brushes and thin the glazes. A squeeze bottle like a dish soap bottle works well. It doesn't spill as easily. Oh, don't forget to screw the lid on the glaze before shaking when mixing. Yeah, it happens to all of us.
There are many ways to finish a project. Looking to finish a textured surface like rock? Apply glaze then wipe off the glaze leaving the color in the crevices. You can use a sponge to apply glaze. To finish the inside of an item, thin the glaze with water and pour it inside, roll it around and dump it out. Let it drip for a few moments and your done.
Hope this is helpful and stop in for visit or sit down and do a project.