How much to use:
Use 1 pound of chicken wings (for chicken or turkey stock) or one pound meaty bones, like neck (for beef stock or lamb stock) for each cup of rich broth you want to end up with.
How to salt :
Do not salt until the very end of the final reduction, if then. Most of the time it’s better to salt the sauce for which the stock is intended.
Any quantity of any seasoning will be concentrated as the stock reduces in volume, so start small.
A similar caution: for long-simmering stocks, start with less rather than more of any seasoning. More can be added anywhere during the process, but too much can’t be subtracted.
When it’s enough:
To tell when the stock has simmered long enough, taste the meat in the stock. When the meat tastes like a paper bag, you’ll know all of the flavor is in the stock. Strain, then cook down the resulting stock until flavorful enough to suit. Usually, between 2 and 5 hours is enough for the original cooking, depending on the quantity. Fish stock generally simmers only 20 to 30 minutes even if the flesh still has flavor.
Some basic additions:
Use carrots sparingly, they tend to make stock overly sweet.
Use a few fresh or canned tomatoes, which add freshness and cut ‘fatty’ richness.
Add a few whole allspice for subtle supportive depth.
Add whole black peppercorns (depending on the amount) to support other flavors.
Add onions, halved through root end.
Add celery stalks (with leaves for extra savory-ness).
Other adds and fixes:
A splash of marsala or madeira is nice for turkey stock; brandy for beef stock; white imported vermouth for fish stock.
A few fennel seeds perk up fish stock.
Leek adds buttery-ness to chicken stock; use some dark tops as well as the white bottoms.
Deeply caramelized onions add depth to a ‘weak’ meat or turkey stock.
Some bouillon crystals or cubes can intensify a thin chicken stock…but do it before salting because the bouillon is salty. Or, just boil down the stock (if you don’t need a certain volume) to concentrate the flavor.
Bottled clam juice is good to extend or brighten fish stock, but watch the salt. 
