I usually sand the pads against the direction of rotation, with 100 grit coated sandpaper. Same with the rotors, in kind of an X pattern, lightly, just to break the glaze. Knocks the high point off of the scratches. Take it easy with the brakes for a couple hundred miles, so you don´t glaze them again.
You can buy a sound/vibration dampening silicon for the back of the pads, also a teflon membrane. Also have seen copper foil and copper grease used. The sanding and the silicon usually get the job done.
Some brakes absorb moisture, that makes them catch and screetch. Usually goes away after warm up. Might have a look at the teflon/plastic inserts in the rods the caliper rides on. Have often seen them twisted or slipped in the XJ, binds some.
The sanding technique also works, with the rears and helps stop one side grabbing more than the other. Brake machine tested methode. A touch (very little) of grease on the contact points, between the shoes and backing plate. Might help, sure can´t hurt and is a step in the, by the book brake service.
Glazing of the metal and pads, the resulting vibration are usually the cause of brake noise. Some pad/shoe compounds are worse than others.
The sanding methode is in the old Dodge truck manual and taught to me by an old timer, that was a master (expanded the family business to the west coast, name was Mr. Ray). He had a whole shop full of disc and drum turning machines, he usually chose sandpaper.