The Eucharist is a gift Jesus gave us to nourish us and join us to him. It is His body and blood, His very soul and divinity. We should not take Communion if we are not properly disposed to receive it. Instead, we should make a Spiritual Communion, in which we ask the Lord to come into our heart as if we had actually partaken in His sacred meal. The folks at New Advent posted a wonderful guide by Fr. John Hilton in Westminster, CO that describes when you would need to make a Spiritual Communion and how to do so.
If you are not Catholic (yet!), have been away from the Church for a long time and have not been to Confession, or are in a state of serious sin, this could be a big help for you to further your relationship with Christ, while you are trying to overcome your sin. Common serious sins that keep many people from the Eucharist include such actions as: using contraception, marrying outside the church, other sexual sins, such as adultery. Of course, any serious sin (mortal sin) separates us from God and being able to receive Christ into our body.
If you are able to go to Confession and receive the Sacrament of Reconciliation, that is the first place you should go. If you are not able to go to Confession then make an appointment with a priest you can be comfortable with anyway. He can help you. In the meantime, a Spiritual Communion is an excellent way to begin. If you are serious about changing your life, Christ is serious about helping you.