Oriki provided an excellent answer. I’d just like to add one thing. Ship skills offer extremely powerful bonuses when compared to other skills. The tradeoff is that ship skills apply to much narrower range of ships than general support skills will.
For example, each rank of the Gallente Frigate skill will give the Tristan 1.5 ranks worth of motion prediction, 2 ranks worth of drone durability, and drone tracking speed, which has no dedicated skill that can improve it. Very powerful indeed. Unfortunately, the Gallente Frigate skill only applies to about 20 ships, while motion prediction applies to any ship that fits guns, and drone durability applies to any ship that fits drones.
Of course, you don’t want to neglect your general support skills either, as you’ll get a lot of mileage out of them, and their cumulative effect is still quite powerful. But, I wanted to make sure you knew just how powerful ship skills were.