Two years ago, our lawn was about 50/50 weeds and grass, with a lot of bare spots. Even if you have a lot of weeds, at least they're
green 
and if you keep the lawn mowed and edged it'll give the appearance from the street of being a real grass lawn while you're overhauling it. Lawns with weeds look the crappiest when they aren't mowed regularly, because the weeds grow taller than the grass, so if you keep it mowed it'll help a lot. Set the mower height to 3 inches. It's MUCH better to water the grass deeply, and less often, rather than a little bit all the time. When you water deeply, the grass roots establish themselves deeper, so they can better survive a drought. Watering a little bit, often, makes shallow weak roots.
Get a good book on lawns, and learn the basics of upkeep. Here's some advice: even though spring isn't the best time to overseed (fall is ideal), you can't go backwards, so you might as well start now!
- Get a sturdy rake, and manually de-thatch your lawn. You want to get that layer of yukky dead stuff out. If you can, compost it, it'll make great nutrients for your lawn! Unless you have a HUGE lawn, don't rent a motorized de-thatcher, they're very rough and can do more harm than good. If you can, pull the big major weeds, and if it leaves a bare spot you can spot patch it with Patchmaster.
- "Top-dress" your lawn with quality topsoil. You want to give the seed something to sink it's teeth into. Buy the kind with fertilizer already in it.
- Over-seed your lawn. Water it twice a day for 2 weeks (yes, really!), and watch the little springs of grass
grow!
- Then, once that's getting established, apply something like Turfbuilder with Plus 2 weed control. That'll fertilize the grass, and start controlling the weeds.
- In the fall, overseed again (don't dethatch again!), and then in early spring apply a pre-emergent weed killer.
And no I swear I don't work for Scotts, it's just that 2 years ago my lawn was a total awful eyesore, and now it's
gorgeous! They have a LOT of good info on their website!
Just a warning, killing the grass and starting all over doesn't always work. We tried that with a service, and you still have to do all the procedures to keep the lawn weed-free.
HTH!
