This overview aims to create an understanding of the nutritional issues concerning patients with cancer and provide evidence-based practical guidance to healthcare professionals (physicians, nurses, and dietitians), caregivers, and all others involved in the care of patients with cancer. The focus of this paper is therefore on providing a simple guide for daily clinical practice. The theoretical background and in-depth comprehensive reviews of malnutrition are described elsewhere. Nutrition plays a crucial role in cancer care. It affects treatment tolerability, outcomes, and quality of life. However, a focus on nutrition is still lacking among oncologists because of insufficient training in nutrition topics received during graduate and postgraduate training and an underestimation of its importance. The consequences of the disease and its treatment, such as anorexia-sarcopeniacachexia, are therefore still often overlooked, underdiagnosed, and undertreated. The authors have summarized the most important challenges, evidence-based recommendations, and common clinical scenarios to bridge the gap between comprehensive guidelines and clinical practice, where brief concrete advice is preferred to systematic reviews. Furthermore, an easy applicable overview is provided, which can be used as a guide during daily routines.