Concerning that slightly below average gun accuracy, what ships are you using, what nation and the problem distance you typically engage a target? Study each of your ships specializations, what its best at, the pros and cons. Some of yours may have a high dispersion at long range. But it sounds like your just giving a bad lead on your target if your only hits 3 of 12 on average. Play around with your crosshair options too, you have like 10 of them in the control settings. Co-op battles are the best way to practice your lead and aim in my opinion. Random battles get way more psychological where players actively screw with around with you, zigzaging to evade fire, and faking a turn, not good for general "how to aim" practice- Anticipating a players movements using wasd hacks is always a pain. But spotting an enemy bot who is traveling 5 degrees to starboard as opposed to traveling perfectly parallel to your scope can be hard to differentiate at a distance, yet is enough for your salvo to completely miss it. So start with this.
Best option before practice would be to watch youtube vids on crosshair alignment. People use the notches for a rough guestimate for finding bearing after speed has been matched, I commonly fire one shell as a marker then follow up with a full salvo once I have enemies bearing down and can anticipate where the shells will land. Train with one ship at a time repeatedly so its playstyle is memorized.
As for your ships, search for youtube reviews by seasoned players that use your ships, watch how they are utilizing it in battle, and of you see something you like, modify it to your own playstyle. With some ships the shells are accurate but will have a high arc, others with poor dispersion but hard hitting. Bottom line, find your ships niches, find what you like more importantly. Jingles is mostly entertainment but he does thoroughly review some of the more popular higher tier ships. Peacekeeper and Noster are great for starters and every ship I unlock I look at sometimes a dozen gameplay vids on it. Avoid winging it, watching others play helps eliminate bad habits that can develop playing a ship that I have no clue on how to use. Hope this helps a little.