Are there any DIY methods for stain removal that actually work?

Alittle more information would allow me to help-

Q: What is the stain, what is the material and how long has it been there?

Classifying stains-

a) Organic stains- these include proteins and fats, body oils, mould yeast, bacteria, bugs and carbohydrates. Organic soil is cleaned with an alkaline (pH 8+).Most of the stains found in the vehicle interior are of an organic nature and require an alkaline type cleaner. Some organic stains (i.e. blood, vomit, urine) should be removed with an enzyme type cleaner and a disinfectant applied to the area

b) Non-Organic stains- mostly found on the exterior of the vehicle, hard water scale (calcium) lime deposits, Road tar, grease and oil film, and require an acid (pH 6 or less) type cleaner.

c) Petroleum soils - substances that do not contain water, nor are they miscible, these soil types include, motor oils, and crease and road tar, and require a petroleum-based solvent type cleaner.

Stain Types-

a) Water Soluble Stains- These stains can be dissolved in cool water or loosened with water based cleaner, coffee; soft drinks, cocoa and chocolate are good examples.

b) Oil soluble stains- These are stains that are comprised of oily or greasy substances, which include cooking, oil from fried foods and suntan oil.

c) Combination Stains- These stains contain both water based and oil-soluble properties. Cleaning these stains require treatment with a petroleum solvent followed by water based cleaning solution.

d) Unidentifiable Stains- Sometimes stains cannot be identified. Treat these stains like a combination stain. Clean with a petroleum solvent followed by water based cleaner.