If you find yourself dealing with a lot of conflict with others, you would probably benefit from some assertiveness training and conflict resolution skills. Assertiveness isn't just getting your needs met, but learning to do so in a way that respects other people's needs as well. Learning these skills could reduce the level of conflict you experience in your relationships and increase your ability to maintain a supportive network of friends, both of which can significantly reduce the level of stress in your life.
If you don't experience a lot of conflict, but tend to do what others want--at your own expence--you may think you're doing okay in your people skills because you don't experience a high level of interpersonal conflict, but you may be feeling a high degree of intra personal conflict because you're not speaking up for yourself and getting your own needs met. The problem with this is that, not only are you not getting what you need, you're probably growing resentful inside, and this may cause you to finally lash out at the very people with whom you're trying to avoid conflict. You would probably benefit from some assertiveness training, which would teach you to get your own needs met in a way that is respectful of others as well. These skills could enable you to nurture yourself and maintain relationships that are truly mutually supportive, both of which can significantly reduce the level of stress in your life.
The following should help you in dealing with conflict and speaking up for yourself: