You can paint a faux wood grain pattern onto nearly any piece of furniture, regardless of the materials the piece is made from. Metal cabinets can be made to look as though they are constructed of fine wood. Plastic and resin chairs can be wood grained, too. Even furniture that has been painted so many times that the natural wood grain is no longer visible can be restored, in a sense, without time consuming paint stripping. There are many wood graining tools available to make this faux finish.
Research wood grain patterns. All woods have a signature grain pattern and colour palette that needs to be honoured. A "bird's eye maple" wood pattern, for example, is completely different from a "quarter sawn oak" pattern. Study photographs of classic examples of wood grains and choose the pattern most suited for your needs.
Purchase a suitable wood graining tool. These tools, which look like small hand-held rakes or combs, come in a variety of patterns. You can often find a good selection of these tools at home improvement and paint stores. Even more patterns are available from speciality dealers on line. Compare the grain pattern sample associated with a tool to your ideal wood grain pattern choice.
Base coat the furniture piece with one or two "wood" tones. Wood is never one colour: use more than one colour on the furniture piece and "wet blend" the two colours at the edges where they meet. The "wet blending" technique uses two brushes, one brush for each colour. Change the brush and the colour as you work and allow the two colours to blend in together at the wet edges for a natural look. Let this base coat dry thoroughly.
Apply a thin coat of a darker "grain" tone paint. Wood grains are created in natural wood by the presence of darker growth rings and graining is usually darker than the surrounding "clear" wood. Apply the grain tone over the dried base coat, but do not allow the grain paint to dry. Work in sections if the furniture piece is large: covering the entire item in the grain tone paint will risk it drying before you can achieve the wood grain effect with the tool.
Use the wood grain tool on the still-wet grain paint. Press the tool against the surface and drag it along the furniture piece in a smooth motion. Don't worry about "wavy" grain lines as they occur naturally in most woods. The wood grain tool will remove some of the darker grain paint and leave a distinct wood grain pattern behind. Wipe off the tool frequently to remove excess paint.
Work in one direction. Choose which direction the wood grain will run and then maintain that direction. Most large furniture items, like big dressers and some tables, are grained lengthwise, from the farthest edge of the piece to the other edge of the piece: graining "across" the length (creating shorter "boards") is not realistic in most cases.
Add more wood knots if appropriate. Use your darker grain colour and an artist's brush to paint in subtle wood knots. Wood knots are never perfectly round of course. They are usually tear drop shaped.