What you should have done back then was to go over it again with the mower until it was all mixed down into the sod.

For now the bugs will eat the decaying matter. As for new grass you are fortunate to live in an area where spring grass seeding is not a problem. You could rake with a hard rake to loosen the dead grass and the very top surface of soil. Scatter the seed and roll it down or walk on it all to press the new seed into the surface. Then if it s not raining/misting every day, water it lightly 3x per day just enough to keep the seed and surface moist. Don't saturate the soil and don't wash the seed away. The seed you get at a hardware store is likely to have rye, fescue, and possibly Kentucky bluegrass. These three grasses have three different germination times. Rye sprouts first in a week. Fescue sprouts in 2 weeks, and KBG takes 3 weeks to germinate. Keep watering daily as long as it takes to get about 80% germination. Then start backing off on the watering frequency and go up on the duration. Eventually you would be watering 1 inch every time you water. How often you water depends on the temperature. If your summer temp is in the 80s, then water 1 inch every 2 weeks. The soil surface will dry out completely before the grass roots need water. When you water deeply and infrequently like this, the roots will grow down deeper to get the moisture lower down.

No KGB in western Washington :-) And if you have a heavy thatch layer you will need to remove to have any sort of successful over-seeding germination. Seed needs to be in contact with the soil.

In addition to dchall's other comments, mow often and mow high. Bag up the clippings or better yet, invest in a mulching mower. In the PNW you may sometimes need to mow as often as twice a week in spring when the grass is in an aggressive growth mode, reducing down to once every 10 days to 2 weeks in summer when the turf grasses go dormant. And then picking back up the frequency in fall as growth begins again.

Here is a photo of the my poor lawn... :(

these are some of the worse spots

but the rest isn't looking so great neither, a lot of thatch for some reason

Thanks dchall & gardengal! I'm a total lawn care noob this is our first home. I enjoy DYI projects so I don't want to give up just yet. Hopefully I can turn this around.

@dchall "What you should have done back then was to go over it again with the mower until it was all mixed down into the sod."

>> that makes total sense now...

@gardengal "mow often and mow high. Bag up the clippings or better yet, invest in a mulching mower."

>> how high is appropriate for PNW? I think mine is a mulching mower, but i think the grass was too tall. I was mowing too short at first so I let it grew out but waited too long.

I just uploaded couple photos, just how hard should I rake? In the top photo, the decayed clipping is really wet and caked on. By doing so, do I need to worry about further ripping up my lawn?? The rest of the lawn is not as terrible, see 2nd photo, but you can see there are still alot of thatch and the grass just not growing properly. Should I rake these areas too to remove the dried dead grass?

I actually bought a thatch rake off Amazon and I tried to remove some of the thatch layer last season but the soil still wet and it ended up ripping up the dirt. So I am a little nervous about doing that again.