In this paper, two tools to improve the performance of the NEH-based heuristics for the flow shop problem with and without buffer constraints are proposed. The first tool is the use of the reversibility property of the problems considered and the second one is a new tie-breaking strategy to be use in the insertion phase of the NEH heuristic. In addition, we have analyzed the behavior of five initial solution procedures for both problems. The analysis of results confirms the effectiveness of the measures proposed and allows us to recommend the best ordering procedure for each one of the problems.