To keep a nice looking lawn is a constant endeavor. This is what I do each year.......
-Dethatch....use a rake and get up all the dead grass/leaves ect.
-Aerate....you can rent one at a local tool rental shop or Home Depot. They are pretty easy to use. Watch out for invisible fence lines and sprinkler heads. You can go over your yard twice in a cross pattern.
-Fertilize....I use Scotts fertilizer (I use Lowes) and a broadcast spreader. Stay away from a drop spreader. If you aren't paying attention you will get tiger stripes in your lawn where you have missed with the fertilizer. I fertilize 5-6 times a year. Scotts has a pretty easy system with months to apply the different applications. Scotts has good information on their website. I fertilize every 5-6 weeks. I also fertilize a little more than the recommended setting. If you use a Scotts spreader and it calls for a spread rate of 3 1/4 I will do 3 1/2 or 3 3/4. Just don't go crazy with the fertilizer or you can burn up your lawn.
***If you are going to seed don't use the crabgrass preventer "pre-emergent" fertilizer, it will not let the new seed grow. Just use the turf builder or +2 weed control
Overseed....buy some good grass seed and use the same spreader to spread the seed. The seed and the fertilizer will drop down in your plugs. You really can't spread too much seed but don't go crazy!! Try to time all this when there is rain in the forecast (that night or next day). Sun will dry your seed out and too much rain will wash it all away. You can also seed/patch bare spots. I like to get some top soil and spread it in the bare spots, spread seed over the top soil and spread some more top soil over that. I then spread straw over the area to prevent the sun from drying things out. Then WATER...a couple times a day. Don't let your new seed get dry!!!
Weed control....I use a simple pump sprayer from Lowes ($20 found in paint/deck stain section) and buy the large bottle of Ortho weed B gone CONCENTRATE!!! You mix the concentrate (a little goes a long way, just a splash in the sprayer) and fill the rest with water. You now have a TON of weed spray to walk around the yard and spray every broadleaf weed you see. MAKE 100% SURE YOU DON'T BUY THE STUFF THAT KILLS GRASS ALSO!!!! Around April you can fertilize again with Scotts turf builder with weed control.
Mowing...As previously mentioned, mow LONG. 4" or 4 1/2 ". This will be the highest or second highest setting on any mower. The longer grass will provide shade for the grass roots and prevent it from burning in the sun. Longer grass also chokes out weeds. Weeds grow in the bare spots of your lawn.
Spring and Fall are good times to aerate and seed. Some do one or the other but I do both. It looks like you have good shad in the front yard which will help!! You can also spread some insect control (granular like fertilizer) to kill grubs ect. Some might even do a soil test but I don't know too much about that!! I'm no expert so take bits and pieces of what everyone is saying and figure out what works best for you. Once you have a general idea down it's not difficult just a little time consuming!! Well worth it in my opinion!!!