In the northern hemisphere, we're heading into the hot part of the growing season right now -- and most of our lawn grasses do better when they're planted in early fall. Do you have other grass that you'll need to have the new stuff blend with, or are you starting a new lawn entirely?
The best thing you can do to help your new lawn establish well is to wait for the right time to plant. In the meantime, you can spend the time preparing the soil for planting, deciding exactly which species you want to plant, and perhaps growing a quick "cover crop". Even if you manage to get your seed germinated this time of year, the water bills to keep the seedling grass going will be $$$$.
If you're in the US, almost every state has a series of publications on growing good lawns in that area... just google the name of the state, lawn and restrict the site to .edu and you should get some good help.
Otherwise, I'm going to give you about the same advice I gave to another new gardener the other day: Find a copy of "Rodales Chemical Free Yard and Garden", author is Carr. It's about 15 years old now, so you can find used copies cheaply. Read the sections on soil, climate and water at the beginning of the book, and the chapters on lawn towards the end and you'll have a good idea of what types of grass you want to grow. For instance, bentgrass makes a lovely lawn, but to take care of it properly, you'll be mowing nearly every day. But if you live in an area with not terribly wet summers, have a sunny lawn, and don't like to mow, you might choose buffalo grass, which won't need watering once it's established and you only have to mow once or twice a year. http://www.bbg.org/gar2/topics/sustainable/handbooks/lawns/3.html
