You begin with the soil. Try to figure out what kind it is. Cooperative extensions will do soil tests for you and make recommendations, contact yours. You have to get a box to put the soil sample in and instructions on how to take a sample to put in the box. Then take to Cooperative extension and they will send to a lab and in a couple of days you will have comprehensive results. Invaluable.

Also look at the light conditions, where the sun hits (or doesn't) and when. I think your lawn needs to be totally reseeded. Now is the time to do it. Figure out if and where you want any garden or shrub beds, also trees. Plant trees first, get small ones, they grow fast. Plant for the mature size of the tree so don't plant your plants close to the fence or house. Enjoy!

P.S. My dad swears by "Lawncare for Dummies." You might want to get a copy of that book.

Since your in MN and spring weather is just hitting with the snow finally leaving, there are a few things you can do as the sun starts to be out longer and temps warm up. First priority would be getting on the leaves and sticks out of the yard so it's not smothering the turf. Depending how many leaves/sticks this could be done a few ways. You might need to stick to rakes and blowers instead of a mow and bag. Either way, once the yard is cleaner take a look at the ground, it might be so compact and shady that just throwing seed down won't help much.

If you're really serious about getting fuller and thicker turf, you might be be best having a local company that takes care of turfs recommend a course of action for you which could include spring aeration and seeding, and maybe fertilizer. If the soil isn't to bad though it might just need some seed and maybe some fertilizer.

It's still relatively early landscaping season in MN, the grass just turned green here in central Iowa within the last two weeks. So you should be able to do some work to get things looking better before grasses really start to kick in.