Late summer/early fall is a better time to seed. It gives the grass more of a chance to establish before the heat of summer hits.

I did seed in early fall. should i not seed again now. what about fertilizing. thanks for your help.

If you seeded in the fall and you need to seed again, I think you may have bigger problems than timing.

I'll assume you have a lawn with Kentucky bluegrass (KBG) and/or tall fescue. These do best with about 3-4 lbs of N per 1000 sq ft per year. If you mulch mow, you should be getting about 1 lb of N from the clippings. Wait until the grass has been growing for a while before fertilizing the first time. You'll probably get good results if you fertilize once in May, then once in September (August if it cools off early) and once late in the fall, after the grass has stopped growing, but while it is still green.

If you seeded with KBG, even if there are some bare spots, they should fill in. The exception to this is if those spots are in deep shade. If that is the case, you might want to consider planting fine fescues in the shady areas (but they'll do best if you wait until fall, also).