Remove bones from fish

the tool

No secret, you absolutely need a pair of fishbone pliers, it's really the essential tool with enough strength to be able to catch and remove a fishbone, usually very well hung.
You can use a pair of universal or fine-nosed tweezers, but it's not very practical (don't even think about recycling an old pair of tweezers, you won't get anywhere).
If you have to buy one, go for a stainless steel one, like the one on the picture above.

Finding the fish bones

This is not so easy, as they are usually almost invisible.
The best way is to put the fillet or the fish in front of you (on a plate if possible) and to pass your finger along the flesh, if the bones are not visible, on the other hand they can be felt.

Removing them

That's the trick, it's not obvious but there is a kind of "direction", fish bones are generally oriented from the head to the tail, from the central bone and slightly curved, schematically, like this:

Add to this that there is a tip and a point, the tip being significantly larger than the point.
If you magnify it a lot, a fish bone looks like this:

When you have a fillet in front of you, it's the inside of the fish that you see, the fishmonger has cut the flesh along the central bone, and then all the other bones are cut off as well.
So they are in the flesh like this:

To remove them without too much difficulty, you have to go in the right direction with the pliers, grabbing the big end, and pull in the opposite direction.

In other words, in the direction indicated by the green arrow, but especially not in the direction of the red arrows.
Well, it wouldn't be dramatic either, but 1) it will be harder and 2) you might tear off some flesh with the edge, which would be a shame.

So you have to do that for all the bones, until you run your finger over them and you don't feel any point, then move on to the next fillet.
Yes, yes, it's long and painful, but what a pleasure afterwards at the table...

To sum up: To remove the bones from a fillet or a fish steak, you need a good pair of bone grippers, and pull them in the opposite direction of their location.