Theory, eh?
1. Make sure your maths is up to snuff, so that you can manipulate equations easily. Don't skimp on this. Maths is the best tool for making the behaviour of electricity understandable, just as a screwdriver is the best tool for tightening MCB screws. Play with equations, rearrange them, find applications for them, explain them to others.
2. Experiment with electricity or electronics in some form. Make circuits, build electronic hobby kits, do something that actually works and is fun. It doesn't have to be specifically electrical installation work.
Now here's the important bit, IMO.
3. Continue playing and matching the theory to the practice until they blend naturally together. You will start to get an instinctive feel for the real-world significance of all the units and quantities that you are writing about on paper. You probably have a feel for how big a pint is, and what happens when you try to put a pint into a half-pint glass. Do the same thing for an amp, a volt, an ohm, a coulomb, an amp-hour, a watt-hour etc.
Example: When you are driving along a road, it is obvious that the destinations ahead of you will get closer, while the ones behind you get further away. You don't have to do any maths to work that out and you never get the minus signs wrong and come up with the opposite conclusion. That is because you have had so much life experience of going towards and away from things that the concept is completely natural to you. But it can also be expressed as S = (v+u)/2 * t, it's just a different way to think about the same phenomenon. You want to be in the same position with Kirchhoff's second law.
4. Much electrical crafts teaching stresses the importance of regulations and you will learn a lot that is needed to comply with them. But electricity doesn't obey regulations, it obeys the laws of physics. For historical reasons, many countries have different electrical regulations but electricity obeys the same laws everywhere. Keep a mental balance between the theory that is needed to comply with regulations (e.g. how and why Ib <= In <= Iz) with the theory that makes electricity tick (e.g. how and why Q=CV).
5. Keep asking questions!