Skills to train to lvl 5

Electronics - Improves CPU for all ships, allowing more/better modules to fit.
Engineering - Improves powergrid for all ships, allowing more/better modules to fit.
Signature Analysis - Improves targeting speed.
Weapon Upgrades - Lowers CPU requirements for gun or missile modules. See also Advanced Weapon Upgrades.
Navigation - Increases base speed for all ships. Better chance of catching up to, or escaping from, enemies.
Evasive Maneuvering - Increases ship agility, reducing align times and allowing closer orbits at higher speeds.
Energy Systems Operation - Increases capacitor recharge rate, which is necessary for almost all modules.
Energy Management - Increases maximum capacitor capacity.