Real red rust can only be achieved on iron and steel. (Stainless steel is much more rust-resistant than regular steel.)
Iron and steel can be rusted a number of ways. Depending on how uniform of a result you want, you may want to clean your item with degreaser and or acetone first. Acetone will also help remove any clear protective finishes on your item. Heat will speed up any chemical reaction. Allowing your metals to heat in the sun will help speed things up. For galvanized steel, first immerse in vinegar overnight to weaken the protective layer.
Bleach is corrosive to metal and will oxidize (rust) it quickly.
Hydrogen Peroxide, Vinegar & Salt
You can spray this mixture onto your item. A suggested recipe is 16 oz hydrogen peroxide, 2 oz white vinegar, and 1/2 tablespoon of salt. Prepare your item by coating it in vinegar several times first (like with a spray bottle). Then apply the mixture for an immediate rust result.
Iron-based Rust Paint
There are a few products that actually allow you to paint rust on. Iron-based reactive paints can be applied and then activated to turn rusty.
Rust-Colored Paint over Texture
Rust-colored spray paint primer is commonly available. Acrylic arts and crafts paints are also good for smaller projects. Use more than one color or shade of rust for a more realistic effect. A reddish brown for low-lights, a drabby orange color for highlights. A rusty paint job looks even more realistic when texture is added. Try spray texture for wall touch-ups, 3M Spray 90 adhesive, dirt mixed with paint or adhesive, or a little bit of spray foam insulation for really nasty texture.
Examples of good rust paint pair combinations:
Burnt umber and raw umber acrylic paints by Liquitex
Berry Wine and Honeycomb by Folk Art
Textured Spray Paint
Rustoleum offers many colors of textured spray paint (including MultiColor options). These can be used right out of the can for textured, brown rust effects.
One unconventional way to create a rust effect is to sprinkle cinnamon onto fresh paint, or spray adhesive. Sprinkle it between layers of paint for a more complex effect.