Non-orthogonal multiple access (NOMA) is a key energy and spectrally-efficient multiple access technique. In this poster, we analyze the adaptive multi-user clustering (AMUC) for the downlink NOMA systems in the presence of imperfections in successive interference cancellation (SIC) and propose various user arrangements and power allocation strategies. Given a cluster arrangement, we initially allocate the minimum required power and ensure each user in the cluster achieves at least orthogonal multiple access (OMA) rates. Then, we present fair, greedy, and max-min power allocation strategies to utilize the remaining power and achieve various trade-offs. Through numerical evaluations, we show that the proposed user arrangements and power allocation strategies achieve a significant improvement in network performance when compared to the state-of-the-art algorithms.