Use a tool like Pyfa - The Python Fitting Assistant to see how different skills and modules impact your fits. You should train Power Grid Management and CPU Management to level 5 early in your Eve career - they are core fitting skills.
If you still need additional power a low slot Power Diagnostic Unit will give you a modest boost to power, capacitor and shields. A reactor control unit, also low slot gives a larger boost to power or use a Medium Ancillary Current Router rig. There is also the “Squire” Power grid Management implant.
Last, but not least, if a large shield extender is causing your power problem, train the Shield Upgrades skill.