well there's a couple things to consider, lets start with your FCS.
since most new players play with auto aiming fcs, i'll asume you use it as well.
Auto aim makes aiming easier if you have to get used to your ship turning and how your turrets turn, but it's not the most accurate way to aim.
with auto aim your guns are set to aim at some space from eachother which means you can hardly every hit all 4 guns at ones (unless you're shooting at a larger target).

to make aiming more accurate you need to cross your guidelines over your target, so all shells are most likely to hit close to eachother (depending on spread).
But to do so you will need a "aiming FCS" 

"aiming FCS" can take anywhere from a day to a week to get under your controle, so don't give up if it doesnt work out on the first couple of battles. 


something i allways found inpractical when aiming is small guns with a low shell velocity.
if the shells are lobbed onto your targets instead of moving in horizontal lines it gets harder to aim/ you need to do more predicting, and you need to change your gun angles more often.
So if possible try to get a gun with good shell velocity (i'd start trying this from 6", unles you play RM, then the 3"will do). when you start using aiming fcs.
this is usually around lvl 20-25.

and for aiming it's important to have some decent guidelines, which are determined by your BO's bve status, so allways remember to fill the rookies on your BO when you lvl up, otherwise your guidelines will stay short, which will give you a hard time aiming in the long run.

there's probably a lot more to aiming, but i'd say these are the basics.. 

It's better to learn how to sling shot from the start, that sorts out the men from the boys.

i.e turn into target (z) front guns fire, turning away from target (c) rear guns fire.

You wont be using this all the time, but if ur starting to learn manual shooting, you may as well start as you mean to go on.

Alot of it is predicting where the ship is going to be next, in the few seconds it takes your shots to travel to the ship you are firing at, but that comes with time.

Hello

Use manual aiming.

1) Go into training missions. Do them (with manual aiming FCS) at least 10 times each

2) Read as much stuff on this forum, about your Nation that you chose as BO. AFter that. Read it all again

3) Tactical advice, if you look very close at the gun 'guidelines', theres dots. Depending on nation, most guns angle at 39-45 degrees, so those are your 'zero' ranging markers. Fire a shot off, you will see where shells land. Thats your 'zero' - at that angle.

4) The trick is, to 'know your angles'. When ships are rushing you (ie charging at you), all the guns have various degrees that the guns must be lowered. Thats why most people are experts in 1-2 types of ship :)

5) After all the above, there are dozens of people in this game who would give a short in game teaching lesson of manual fire

Rgds

farmdogeu

in what level or ship i should change fro auto to manual? thx in advance.

beside all those advices, important about how to shoot, you must have in mind another point important as aiming: Spread.

No matter what you do, most guns will reach the best possbile spread  just when your sailors reach a high level, over 90.

Dont panic with that, the system is it. 

I learned manual aiming at CL levels, by learning to AA first. less pressure than in direct combat with another ship. Once you have the gun control and angle adjustments down, you can move on to ship to ship cannon and learn your angles/range.

Matter of fact whenever I come back to the game from a prolonged absence, I still like to run a AA ship for a little while to refresh my muscle memory before jumping right back into a BB.

I agree with Nikki. Try Emden, Emerald or Omaha if you want to practice manual aiming. It's a nice way to train yourself, and your crew too.

It would be good if we could access a training mission at higher levels so that we could practice firing long range guns without actually being in a battle.