Thank you for the photo of your lawn - your garden looks lovely! To overseed you should use a mix of different seeds suited to your climate. I am going to guess from the plants in the photo that you live in a cool summer climate so a mix of fescues and perhaps some bluegrass might be best. The local nursery or garden center will sell a lawn seed mix for your particular climate and my advice is to invest in the most expensive grass seed. This way you know you are getting the latest in grass seed improvements as there will be a royalty paid to the newest seeds and it is worth the higher price for quality seed. Grass seeds needs to be kept moist at all times the first few weeks so cover with peat moss, compost or purchase seed with a paper/tissue mulch already mixed with the seed. Just keep the seed moist and you should have good results. Keep growing, Marianne Binetti