Look at Purdue University's Turf Grass site and it will answer a lot of your questions.
http://www.agry.purdue.edu/turf/pubs/
You really don't want to seed or over fertilize at this time of year. That should be done starting in September. Depending on what turf grass is growing in your yard, you need to mow at the correct height. If you have anything other than Zoysia, that means 2 1/2" to 3 1/2". This keeps the weeds seeds from germinating, but it also means you're cutting the grass once a week.