Take a picture or five and go to your local lawn and garden store that is family owned, get pictures of the house as well, they can help you work out a plan to get it in shape and tell you what to plant where and what type of work needs to be done

Depends on where you live and if you plan to use chemicals to achieve your goals. Personally, I prefer hand-digging the broadleaf weeds and mowing the rest. The alternative is to use a product designed to kill weeds.

If you live in an area with a rainy spring you still have time to do some rehab. If not, wait until Fall. If there is thatch you can rent a dethatcher or rake it out. It wouldn't hurt to aerate, too. Throw down some good quality grass seed if needed. Then fertilize (I prefer organic) and throw down some nice compost. Give your lawn plenty of water during the growing season. I like using a mulching mower so the grass clippings stay behind and help feed the soil.

If you can live with a less than perfect lawn, over time with a little TLC you can make it much better without using harsh chemicals. Mine is looking pretty good if you don't look too closely! Enjoy.

Mow it every week, that should keep the dandelions down. I believe in spraying weeds but I know that is not for everyone. Depending on how much of the "big grass" you have I would hand pull it. You cannot use pre emergent if you plan on seeding the bare spots. I rough up the soil in the bare spots, throw down some seed and then a light layer of topsoil. The see can still show. Then keep it wet.