Sometimes baked-on grunge just won't succumb to soap and water. In this case, you can try a solvent-based solution. Mineral Spirits are popular, as is gasoline or kerosene.
It pays to be careful with solvents - and not just because they soak into your skin! Solvents dissolve rubber, plastic, and other non-metal parts very quickly, so make sure you know exactly what you're cleaning!
You can use solvents for cleaning in a bucket, but for about $100, you can buy a parts washer with a pump and jet, and this makes the solvent cleaning process much easier. Be sure to invest in a good set of chemical-resistant gloves as well. The latex shop gloves you might be using simply will not stand up to this kind of stuff - even the nitrile ones.
For a good all-purpose cleaning solvent, I like to use biodiesel of B50 or higher (B99) concentration. There's less harmful stuff in biodiesel than in #2 petro-diesel, and it actually works better as a solvent. But it does attack natural rubber, so pay attention.
Get yourself a good selection of scrub brushes with steel, brass, and nylon bristles. Also, a selection of kitchen Scotch-Brite pads will work wonders.
One last word - under no circumstances should you use Acetone. This stuff is pretty nasty and evaporates quickly while you're working, and you inhale it. Plus, it doesn't work any better than biodiesel.