The Method
The standard method of glazing is the most reliable. Painters complete their oil paintings, and then take a layer of transparent, or lightly colored paint, and paint over top of the oil once it has dried. The transparent paint must be diluted with oil to create the glossy sheen. It can be difficult to get the mixture right the first time, but with experience and experimentation, painters are able to create the appearance of shiny materials in their work.
Standard Techniques
Some painters find it useful to use an extremely thin layer of glazing in their work. This will ensure that glazed object stands out without overpowering the painting. To glaze your paintings, you should go very slowly and be very careful; otherwise, you risk ruining your painting. Another technique that is useful to remember when glazing, is to use complimentary colors. If you're using a colored glaze, try to use a light reflective color that is similar to that of the base. Otherwise, you risk making your painting murky.
Experimental Techniques
A number of experimental techniques also help painters create a glazed look. If the goal is only to create a shiny or glossy look, painters can use a number of other methods and materials. Using different types of paint, such as acrylic, will instantly create a glazed look. Similarly, mixing paint with other shiny substances, such as egg, is another technique that will create this effect. However, this is typically done with lighter paints, such as watercolors. Experiment with different materials, but you should remember to create thin, fast-drying layers, and take care when mixing different substances on the same canvas.
Scumble Technique
The scumble technique is actually the opposite of glazing, but it has a similar effect. Instead of applying a layer of glossy paint to the canvas, painters apply a very thin layer of dry and thick paint over top of the oil paint. The bright colors underneath shine through and create a similar textured look. It's very important to use as thin a layer as possible and a very small brush when using this technique, since it is easy to cover up the oil underneath and ruin the painting. It's better to use darker colors with this technique.