Memorize the symbols. To save space on the diagram and to make them legible to people who speak different languages, schematic authors use a series of illustrative symbols to denote the various integral circuit components. For example, a general capacitor, commonly used in guitar amps, is denoted by two parallel, vertical lines each with a horizontal line of half-length extending from the center.
A potentiometer, which is a variable resistor used in guitar volume dials, is denoted by two short horizontal lines, separated by a horizontal zigzag that is twice the length of each horizontal line, with an arrow pointing up to the zigzag. The arrow indicates that the resistor is variable. A resistor has the same symbol, minus the arrow.
Study a schematic and copy down the symbols. Try to write down the name of as many symbols as you can remember. The characteristics of a schematic varies according to the intended application of the circuit. For example, guitar effects pedals have multiple cathodes, capacitors and transistors.
Learn the values. The values are denoted by numbers and they qualify the symbol that they are attached to. For example, the number next to a resistor denotes the resistance of the component in ohms. For example "12K" next to a resistor indicates that the resistor has a value of 12,000 ohms resistance.
Study a real circuit. Unscrew the chassis of a battery radio and examine the circuit board inside. Make a a list of each component that you can visually identify and draw the component symbol next to it. Trace each wire from its beginning to end to understand the mode of connection. Some circuits do not have wires, in which case unscrew the circuit board from the chassis and flip the circuit over. Follow the conductor strip on the bottom of the board. Make a note of each component that is connected by the same conductor.
Draw your own schematic. Plot a rectangle to begin with, then denote an integrated circuit. Denote wires with straight lines. If two wires are connected, indicate this by drawing a circle over both lines at the connection point.