The usual ratio for bone to water in clear beef stock is equal weights. That is, one pint of water per lb of bones -- or one L water per kg bones.
Roast the aromatic mirepoix (for beef stock, usually just carrot and onion, but celery is okay and leek instead of or in addition to onion is also okay) and the bones together until both are browned -- before making the stock. Browning is an essential part of the process.
If you use strong flavored aromatics (like garlic) or distinctive herbs, your stock will be anything but neutral. Reserve those for farther-down-the-line cooking. Also, keep the amount of salt you use way down as you may want to reduce the stock later for some other purpose.
Put your roasted bones and mirepoix in a stock pot with cold water. Think of stock as an infusion, like tea. Don't boil the stock, simmer it. If you boil the stock it will be cloudy and won't ever clarify. Bring the pot to temp as quickly as your burner will allow, but watch it carefully and don't let it boil for more than a second or two. Reduce to a simmer.
Skim the scum from the stock frequently, until it stops producing scum.