If you've already seeded, you might as well give the seeds a chance to germinate and then reseed in the fall where needed. If you have sandy soil, water will percolate quickly through the soil and the surface, where the seeds are, will dry out. This might mean you need to water more often, but not a lot (just enough to keep the surface moist), to keep the surface wet. Adding organics/compost to the soil will greatly enhance the water retention of the soil and provide nutrients the grass needs once it germinates. One thing you might want to do is have your soil tested by the local soil extension service. This will give you data on how sandy your soil is, as well as, pH, organic levels, etc. A great starting point. Not sure which grass type is "best." I understand tall fescue varieties stand up well to dry conditions, but some don't like the slightly thicker blade and it growing in tufts. It's all a trade-off! Good luck.

2. Water deeply and infrequently. Deeply means at least an hour in every zone, all at once. Infrequently means monthly during the cool months and no more than weekly during the hottest part of summer. If your grass looks dry before the month/week is up, water longer next time. Deep watering grows deep, drought resistant roots. Infrequent watering allows the top layer of soil to dry completely which kills off many shallow rooted weeds.

3. Mulch mow at the highest setting on your mower. Most grasses are the most dense when mowed tall. Bermuda, centipede, and bent grasses are the most dense when mowed at the lowest setting on your mower. Dense grass shades out weeds and uses less water when tall. Dense grass feeds the deep roots you're developing in 1 above.

4. Fertilize regularly. I fertilize 4 times per year using organic fertilizer. Which fertilizer you use is much less important than numbers 1 and 2 above.
   

Seeding is most successful when done in the fall. Just plan for that from now on. Or you could use a mix of Kentucky bluegrass and never seed again. KBG has the characteristic of going dormant (brown) in the winter while fescue stays green. Of course if you are in the Erie area you will have white in the winter anyway.