Too late for prevent, we are in weed and feed mode. Depending on brand, it is suggested that you do 2-4 weed and feeds before moving on to the next step which usually starts in late may to mid june, iirc.
That said, if you weed and feed a lawn full of weeds, you will end up with a muddy nothing in summer.
It all depends on how prolific the weeds and clover are. If it is most of the yard, just let it be for now then tackle it in late summer/early fall, kill it, verticut like a mother, seed, and spread some compost on top of the seed, then feed it like crazy and make sure it stays moist. Once you have cut it several times, start feeding the roots and winterize it well.