The Apostle Paul says that we carry holiness in earthen vessels. The vessel is not fit for what is in it. And we cannot first prepare a worthy vessel and then receive in it the gift of the Holy Spirit.
But we can come to God and openly say to Him: ‘Lord, come! Lord, flow into me! Unite me with Thyself! I know that I am not worthy, but be Thou like fire which burns away the thorns [of sin and imperfection], not as fire that will burn me away completely in the horror of hell.’ And this is something that happens gradually.
If you waited to unite with the Holy Gifts til you became worthy, no one would be able to do it. For a start, one would have to say to the person who says ‘Today I shall go to Communion because I am worthy’, — ‘Oh, no! Not today, because you are puffed with pride or else have lost your senses! More likely than not, lost your senses.’ What else could one say? If a person comes forward and says ‘I am totally unworthy, but Thou became Man in order to save me’ — that is possible.”
-Metropolitan Anthony (Bloom) of Sourozh, taken from his book Coming Closer to Christ: Confession and Forgiveness