Lightweight cryptography is a branch of the modern cryptography, which covers cryptographic algorithms intended for use in devices with low or extremely low resources. Lightweight cryptography does not determine strict criteria for classifying a cryptographic algorithm as lightweight, but the common features of lightweight algorithms are extremely low requirements to essential resources of target devices. In this paper we propose generalized approaches to lightweight algorithms design. Also, we highlight some constraints and recommendations for implementation of lightweight algorithms. Finally, we anticipate several trends in lightweight cryptography.