An observational drawing is a drawing taken from life, not copied from a photograph or taken from your imagination.
The drawing can be a line drawing or rendered as accurately as possible to show the form and texture of the subject. Observational drawings are useful for showing multiple view points, proportion and the objects relationship to its environment.
When you are drawing from observation, look carefully at the environment in which your object or subject is placed. Study the shadows cast onto your object and the ground and look carefully at the direction that the light is coming from.
Cross Hatching is where layers of lines are placed at different angles. Collection of horizontal and vertical lines.
Contour Hatching is where layers of lines follow the contour of the object being rendered. This method of hatching can be used to achieve amore 3D effect.
Scumbling is where you use layers of small scribble-like marks to build up tone and add texture. By changing the direction and shape of your scribbles, you can add more impact to your rendering.
Shadows: The ability to render objects with projected shadows and understanding how to use different light sources can make a difference to your drawings.
Light Source: When starting a rendering of an object, you need to decided where the light source is coming from, as light source creates the light and shadow areas on the object.
Steps for drawing multiple objects. https://www.artyfactory.com/still-life/still_life_pencil.html