A good brine shrimp egg hatch-out will depend on a few important criteria, and at the prices of artemia, getting the best hatch-out you can, will save you substantial amounts of money.
First, the pH in the hatching container should be over 8.0 during the full hatching time. Many people's water will have the pH fall drastically during the hatch-out, so you should test it after 24 hours of incubating the shrimp eggs. You can use some epsom salt and some baking soda to get it where you need it.
Second, salinity should generally be high. 1.023 to 1.030 on a hydrometer is the range you should try for. Some artemia will hatch better in different salinity than others. Measuring tablespoons per liter doesn't work. You need a hydrometer to get this right. After you have determined the correct amount of salt for that type of salt, you can use a measuring cup to get the salt correct.
Third, the temperature should be approximately 80 degrees F. If the container is too hot, the brine shrimp will not hatch as well and it will die easily. If it's too cold, then hatch-out times can be delayed and hatch-out percentages will fall. It is best to keep the hatching containers in a temperature-controlled room or box. Below is an example of a hatching box that uses low wattage bulbs to control the temperature. Temperature can be varied by using different watt bulbs and putting a door on if the room is too cold. The bulb in this box is a 7-watt fluorescent. The second photo shows the brine shrimp hatch-out of our typical Premium Grade with the bulb turned on.