JOEL - This is actually a very personal matter that, unless specified by the Bishop, is left up to the individual according to how they feel about their own worthiness.
In the scriptures we are told:

"For whoso eateth and drinketh my flesh and blood unworthily eateth and drinketh damnation to his soul; therefore if ye know that a man is unworthy to eat and drink of my flesh and blood ye shall forbid him. (3 Ne. 18: 29)

Obviously, if we are guilty of a sin that is serious enough to require confession to the bishop, then we should not partake until we have properly cleared up the matter. If upon self-examination one has doubts about whether or not something needs to be confessed, it would be better to discuss the matter with his bishop. He can help put the matter into perspective and can help one know what must be done to obtain forgiveness and feel good about onesself once more. When someone is undergoing any form of Church discipline, as a condition of their repentence process, they will be instructed by the Bishop to refrain from taking the Sacrament for a certain period of time.
For those sins that don't require confession we need to ask ourselves a few questions. Are we aware of our sins, and are we trying to overcome them? Are we truly repentant? Are our hearts filled with hatred or anger or bitterness toward another, or do we feel at peace? These are some of the questions we might ask ourselves before we take the sacrament. I think that if we truly care, the answers lie in our own hearts.
The Sunday School’s gospel doctrine manual for 1967-68 contains this helpful statement:

"If a person finds himself unworthy and does not repent, he should attend sacrament meeting but have the courage not to partake of the sacrament. Those present who see another not partaking should not speculate about the reasons. We should all accept that one can allow the sacrament to pass by if he does not feel he should partake. One should neither miss sacrament meeting if he is not worthy to partake, nor partake because he feels social pressure."

So, once again, if it's not about a sin that needs confessing, the decission to take or not take the Sacrament depends on how you personally feel about yourself.