If you don't have a soil moisture probe, some simple guidelines can help you decide when to water. Water when grass changes from a green to a grayish blue color, when grass leaves begin to roll, when the grass stays down after being walked on, or when you can't easily push a screwdriver down into the soil a half foot or so. Apply 1/4 in. of water and then check to see if the soil is wet down to 6 in. If it isn't, make another application just so the soil is moist, but not wet or sticky.
Always buy “certified seed”. This is identified by a blue tag saying certified. By spending a few extra cents up front, you will save many hundreds of dollars along with the added aggravation of controlling unwanted weeds later. Choose the right grass seed, sod or sprigs for your situation.