There are different groups of drawings e.g. (i) Interconnection Diagrams and (ii) Schematic Diagrams
The Interconnection Diagrams usually explain how a cable is connected on both ends or how does it interconnects two equipments?
All cables are primarily identified from its given identification number and if it is multi core cable, each core is either identified by numbering or by colour coding. An interconnection drawing very well shows the terminal blocks where its cores are to be terminated. This can be found in Cable Schedule indicating where both ends of a particular cable are connected. These drawings also show clearly the terminal blocks with their location in the equipment / panel. These drawings are easy to read.
The schematic drawings show the whole scheme of a particular circuit (or even the whole grid station). For example a schematic diagram for closing circuit of a circuit breaker will show the all elements (showing conditions for closing) in the circuit. Those elements may be placed in different equipment or panels. First thing is to understand location of such elements, it is usually marked with different shapes indicating particular equipment or a panel and number of terminal of that particular terminal block in the terminal box. Second important thing is to read the schematic diagram in the direction of flow of current in a circuit. It is further advised to start reading a diagram from LEFT upper corner and proceeding downwardly reaching to the lower RIGHT corner of the drawing (as we read any English written page of any book). Thirdly, understand the drawing elements like how the normally close / open contacts, coil of a contactor are shown. What shape represents CTs & PTs, circuit breakers, isolators, lightning arresters etc?
If Mr. Mushtaq, the initiater of this topic, lives near by Lahore, I may offer my services to let him learn how to read these drawings in just a one hour sitting.