First of all, As far as I am concerned, you should master rich components knowledge and be familiar with real products as much as possible. Then checking the schematic and BOM list. Finally, you are going to understand each component from the following points:

1. Components label. Generally, there are markings or silk-screen on components, which can be used as the main basis for discrimination;

2. Silk-screen. Each component usually has unique symbols in the corresponding installation place of PCB;

3. Appearance structure. After knowing enough about the package of conventional components, you can judge from the appearance structure of components easily.

4. Instrument and meter measurement. Even for certain similar components, they can be identified by measuring their parameters.