High-flow nasal cannula oxygen therapy (HFNC) has revolutionized the treatment of patients with respiratory failure in different settings. Several mechanisms of action explain us why HFNC has become a first line therapy for these patients. Some authors have referred to the adverse effects that can occur when we use HFNC and its limitations. However, there are numerous aspects that we should consider when prescribing this treatment and that are not documented in the literature to date. In a Task Force carried on by International High-Flow Network members in Madrid, the things that should be taken into account when put a patient on HFNC were addressed. We will discuss in this article aspects related to the device, oxygenation, humidification, tubing, nasal cannula, alarms and finally, those related to the patient who receive the treatment.