I have a 1992 Ford F-150 Custom.Its takes a while to start and then once started it's shakes quite a bit. What do you think I should do

It only has 90,000 miles on it.

Do a tune up.- probably needs one anyway.
Spark plugs,
Ohm ignition wires
Distributor cap and rotor.
Replace PCV valve
Clean EGR valve
Look for cracked or displaced vacuum lines
Then chase fueling issues. (fuel rail pressure, injectors malfunction) if still missing, while running pull one spark plug wire - if the engine stalls or gets worse, replace the wire and go to the next plug, repeat until you find a cylinder that does NOT change the missing idle and you have found the cylinder(s) that need more testing.

Maybe you have a broken motor mount.

I would start with a tune up… And a new carb.

Take it to a mechanic

Tune up
Check for vacuum leaks.
Take a gas sample to see if there's water in the gasoline.

Hi so it is well over 7 years old what else do you expect a miracle new truck.