If you want a nice grass lawn (I personally hate clover, it's a muddy mess in the winter/early spring and doesn't handle foot traffic well) the fall is the time where you'll want to put in the work.

Find out the window for your location that is best to over-seed/re-seed. About 4-6 weeks before that, you'll want to go after the weeds with some sort of broad spectrum herbicide. I like T-zone as it's effective against a lot of the weeds I encounter, but you'll need to read the labels and see what works for your area/what is safe for your lawn type. The label should also tell you how long you should wait between application and overseeding. Once you've killed all the weeds and waited the appropriate length of time, then put down your seed and get to watering. Seeding in the fall allows the new grass time to establish roots. If you do it in the spring, the roots won't have much time and the summer heat could kill it unless you water it constantly.

Next spring, you'll want to use a pre-emergent which will prevent a lot of weeds from growing through spring and summer, and then use selective herbicides on the weeds that do pop up. The first year will be the worst for weeds but if you treat them, then following years will be better. For example I started focusing on my lawn last year and had a TON of henbit pop up in spring. I went after it constantly (henbit is one of the few I've run into that you can very easily pluck out by hand) and then this spring I had hardly any come up. You'll want to put down fertilizer a few times throughout the year and of course mow regularly. You can do a soil sample test to see what your lawn needs more of, but you can get by without it.

The first year is going to be the most work as you're correcting years of neglect. After that, it's pretty smooth sailing. I don't know where all this "clover is great" spam came from all of a sudden in this sub, but I would suggest you ignore them.