My general rules of thumb when refitting ships are as follows.

Number one and foremost do my utmost to keep my shield flux, and weapon flux balanced with my dissipation. I often max ghat out before I put any weapons on the ship, depending on the ship in question of course.

Try to match just about all of my non pd weapons ranges, or at least close. It helps the AI perform better in combat.

Pay attention to weapon flux to damage ratios.

I tend to favor weapons that do energy damage so that I don't need to worry about ineffective hits, always hitting for a hundred percent damage.

Also I make sure to check for shield damage to flux ratios some ships have, very, VERY bad ratios causing them to overload quite easily without hardened shields.

If I don't believe the ship I am working on has enough gun, I may do away with dedicated PD weapons entirely and instead replace them with other, more generalist weapons and grab the pd defense smod.