just get something pokey that you can poke with... some say golfing shoes or ANYTHING pokey...that'll make holes to aerate with...just keep weeding and keep fertilizing and the grass should spread.

Yanno... I thought I was silly for contemplating golf shoes for walking around the yard. I DID have the right idea! :) Thanks.

It would be best if you could get down 6 inches of so with whatever your using to aerate the soil. Pitch fork or anything else. The golf shoes will help some and are much easier. The next step after aerating is to get some compost down into the holes. Alfalfa pellets is still one of my favorites to suggest for a lawn fert. 20 pounds per thousand sq. ft. It sells for around 8 to 9 dollars a 50 pound bag here in central Texas. Just check you local feed store. Just keep poking along it will look better as time goes on. Good Luck David

Aerate, mow high, do a soil test.

Although, frankly, those bare spots look like they're damp and shady? If so, you also need to select the right kind of grass seed.

If you have clay soil, then pokey aerators may do more harm than good. In that case you'd need a core aerator- pulls up plugs and leaves them. Core aerate, lay down compost and bunny food. You can rent a power core aerator.

Lots of folks will also claim that just compost, bunny food, and maybe ACT will aerate for you anyhoo.

The old golfing 'spikes' have been banned on the better golf courses because they compact the soil over time rather than aerate it,just as pablo suggested. Aeration requires REMOVAL of plugs, not compression of the soil to accomodate spikes.

Spile aerators seldom do much good since they simply push the soil away compacting it further, what may be beneficial is a plug aerator, something that removes a 1/4 inch plug of soil. However, the single best thing you can do is get lots organic matter into that Iowa soil because without that OM your soil will simply slide back together again.
In the meantime set your mower at the highest level you can and mow so that you do not cut off more than 1/3 of the grass blade at any time. The more grass blade exposed to the sun the more nutrients that grass blade can manufacture to feed the crown that will then send out more grass to fill in the empty places, eventually. Mulch mow too, recycling the grass clippings right where they came from will supply your turf with 1/2 the annual nutrient requirement as well as supply a bit of mulch to help conserve soil moisture and help keep the soil cooler which will keep the grass happier and somewhat less likely to go dormant this summer. However the key is to get organic matter into your soil.

That second picture looks like a very shady spot with soil that if ever dry would be as hard as a rock. Great opportunity for a hosta garden!

So after you throw some great stuff on there to invite the worms in (free used coffee grounds from a local coffee shop, grass clippings/bags of leaves left on the curb by a neighbour, etc.), I wouldn't bother with grass. Make your life simple and scout some weekend market for cheap hostas or ask a friend who's got some.

You could also add ferns and other shade loving plants. I see so much potential there and would not bother fighting with grass.

Shade gardens are the easiest to grow and the ones which need the least maintenance. And sometimes the most beautiful!!