First steps in campaign are pretty simple - pirate raiders and RSF scouts die from missiles, ISA scouts are easy to deal with if you keep them away from you.
Stepping up to next level is a bit difficult - pirate warbands often contain Wealthy captains that usualy put a shield or extra armour on their ships. Missiles wont work here as effective as they did before. RSF patrols are much more difficult to deal with due to their powerful Kursk-class destroyers. You`ll need something with long range here (streamers/particle cannons paired with 10-pdr guns work good, just make sure you get extra ammo for them). ISA patrols easily rolled by RSF destroyers with extra PD guns. Just give them extra speed.
I usually start intercepting convoys and AIs once i get at least two destroyers. Pirate Armadas can also be put in this level, but only if you really fill that you can deal with them. Note that Crimson Snakes are considered a pretty much deadly foe for any fleet. They are super-fast and can avoid missiles, their lasers can be a problem to any ship, their armour can survive more hits than any pirate vessel.
SDF fleets are deadly and require you to have a large fleet armed to the teeth. RSF with their Moscow-class BB are IMHO the toughest as this ship can suck a lot of damage before dying. ISA mostly bring missile-heavy ships and fighters into their SDF fleets, so massive PD coverage is required.
Alien mothership usually owns everything. But it can pretty easily be dispatched by any capital ship with at least two large energy mounts and good capacitors. Put two heavy beamers on it, integrated targeting unit and advanced optics and your ship can just sit far beyond the reach of Alien Heavy Blasters slowly tearing mothership`s weapon platforms. Once those are dead - bring in TUs or B-202s and enjoy the fireworks. I haven`t tried UIN United Kingdom yet, but i feel it would own mothership pretty well with its two long range assault drivers and fortress shield.
Rock Fly needs some tactics. Its has no coverage from its rear, so harassing it with fast ships armed with some anti-armor weaponry is a good plan. Or you can always bring in heavy beamers and slowly melt the Fly from afar.