This paper presents simple and practical approaches for controlling the complexity of neural networks (NN) in order to optimize their generalization ability. Several formal and heuristic methods have been proposed in the literature for improving the performances of NNs. It is of major importance for the user to understand which cf these methods are of practical use and which are the more efficient. We will try here to fill the gap between specialists of these techniques and the user by presenting and analyzing some methods which we have selected both for their simplicity and efficiency. We will consider only supervised learning.