Since a signature is required upon delivery, please make sure someone is available at the delivery address to accept the parcel. If you are not home, a courier might decide and try to leave the parcel with a neighbour or take the parcel back with him.
When a courier takes the parcel back with him, there are 2 options. Either the courier will try a second delivery attempt the following business day, or he will bring the parcel to a local pick up point for you to collect. In both cases, a courier will leave a card in your mailbox to inform you of this.
When you're not sure if someone will be available to accept the parcel at your home address, you can also consider using an alternative delivery address like your work address or the address of a friend or family member.