The Novena to the Holy Spirit begins today, the day after the Solemnity of Ascension. From EWTN:
The novena in honor of the Holy Spirit is the oldest of all novenas since it was first made at the direction of Our Lord Himself when He sent His apostles back to Jerusalem to await the coming of the Holy Spirit on the first Pentecost. It is still the only novena officially prescribed by the Church. Addressed to the Third Person of the Blessed Trinity, it is a powerful plea for the light and strength and love so sorely needed by every Christian.
The entire prayer can be found here. Speak Lord, for Your servant is listening.