Obtain Gregorian chant sheet music from your local library or church. Having your own copy of the sheet music helps you to regularly practice reading the notes improves your note-reading skills.
Study and learn the different types of simple note arrangements, or neumes, used in Gregorian chant. Gregorian chant uses square notes that are different from modern musical notation. A single note is called a punctum or virga and can occur with or without a stem. Two notes drawn on top of each other is called a podatus or pes; sing the bottom note before the top note. If the top note should be sung before the bottom one, the bottom note appears slightly to the right of the top one --- this is called a clivis.
Study the complex neumes. Common complex neumes include arrangements of four successive notes going up, virga praetripunctis, and going down, virga subtripunctis Liquescent neumes are groups of two or three notes with a lighter emphasis on the last note than on the other notes.
Read the notes from left to right. If multiple notes occur in a vertical line, sing the notes from bottom to top. If more than one single note occurs in a row, hold the note for that many beats. A dot after a note means you should hold the note a little longer than a single note.
Pay attention to note modifiers. Vertical lines below notes, called episemas, give the note a little extra emphasis. Horizontal lines written above notes mean you should slow the speed at which you sing the note. Gregorian chant has only one accidental note --- the B-flat, which looks almost identical to the modern B-flat.
Read the custos note at the end of a line of Gregorian chant music. The custos note looks like a regular note cut vertically in half and lets you know what the next note on the following line or page will be.