Like Mr. Fury said, there are two main weapon-equipments you should use.
1. Only laser weapons. Those ghost-lasers can be very effective, if used in masses.
2. Only anti-shield and anti-hull weapons.
Personally i like to use normal torpedos, cause they are more accurate than plasmaguns and they deal a lot of damage. And most battles, at least in single player, are not that long, so you dont need to watch the ammo on cruisers and battleships. Of course, dont equip them to frigates and destroyers, they dont have the capacity to carry much of them.
Gatling guns are the right anti-hull-weapons for destroyers and NDF-frigates. They are very accurate and in groups of three or four they can easily rip a destroyer to pieces. Of course, they are useless against cruisers and battleships.
Plasma-guns are good all-round weapons. They deal good shield and hull damage, but fire very slowly and are not that accurate. You can install those on destroyers or frigates too, cause they dont need any ammo.
Enery-torpedos are long-range anti-shield weapons. Please, only use them cruisers and battleships, cause the need much energy. Use them against fort-shields, battleships and cruisers, but please, dont try to hit a destroyer or even a frigate with them

. This weapon is very inaccurate. Sometimes i asked myself "How can this idiot of weapons officer miss this gigantic battleship!?!":

Missiles...well they do a lot of damage, but you need to use them in groups, cause the can be shot down by the enemies flak-systems. They only inflict hull damage, but (the Big Bang missile^^) in a heavy and spectacular way. My tip: Fire them on self-laid nav-points in front of the enemy fleet, so the fleet has less time shooting them down. The missiles have a great damage radius, so youll deal some damage then too, even if you dont hit the enemy directly.
One of my favorites is the ion bomb. Huge damage radius, cant be shot down and needs no ammo. And kills shields like flies^^...
Well, i would call myself an experienced Nexus player, i even build a Nexus-database on the homepage in my sig, but its in german, maybe it still helps you.^^