Selecting a cycle with a pre-wash is generally only required for heavily soiled loads. As the name suggests it extends the wash cycle so uses more energy and water so should only be used where necessary, with soiled workwear for example. In many instances, simply adding an in wash stain remover or Soda Crystals will remove soiling with a standard wash, although it is best to use a hot wash (above 60 degrees) if the garment care instructions allow it.
As with most loads, try to group similar items together and don't place whites or delicate items in with the load.
Pre-washes can also be helpful for parents washing towelling nappies or babies' clothes that have been subjected to food spills, vomit or other baby-based 'accidents'.
To pre-wash clothes in your machine, add a wash powder/liquid to the relevant slot IN ADDITION to the standard slot or in the drum. You may want to use a stain removing powder as detailed on the pre-soak page.