"Oscar_Lives
Grass is thin and yard has moderate weeds. fescue/rye/bluegrass yard
in
Missouri. Should I put grass seed down now or should I put crabgrass
preventer down
and try to encourage growth of the grass I have now? "

You should have applied weed killer in late summer to get rid of the
weeds when they were actively growing. Then you could have overseeded
in early Fall, the optimum time. The next best time is early Spring,
though Fall is far more preferable. Putting down grass seed in
January is worthless, as seed will not germinate until soil temps are
in the 50's.

I'd get the soil tested now and apply lime as needed to adjust the PH.