Stem Length
Normal length is one octave (three and one half spaces).
Stems of notes on leger lines which would normally not reach the middle line of the staff should be extended to the middle line.
When two voices share one staff, stems may go in opposite directions. Stem length may be shortened.
Beams
Beam slant follows the direction of the group of notes it connects; either upward or downward. When notes go in different directions, the beginning and ending notes determine the slant of the beams. As a general rule, the beam slant increases as the interval of the first and last notes increase. The amount of the slant is relative and not proportional and should not exceed a slant of one and one half spaces up or down.
Ties and Slurs
Ties have less curve than slurs and go from note head to note head opposite the direction of the stem when used in single line music. When notes of a chord are tied, each tied note receives its own tie with upper ties going upward and lower ties going downward. When a tie is used in a slurred group, the slur must encompass the tie.
Slurs are placed below the note heads if all the stems go up. Slurs are placed above the note heads if all the stems go down. When a slur covers notes with both up and down stems, the slur goes over the note heads.
When modifying marks such as accents or dots accompany a slur, the slur encompasses the marks.
When slurring a chord on a single stem, use one slur only. When a part has more than one voice, separate slurs are used and are placed above or below the stems.
Time Spacing
A note head indicates when the note begins and the space after the note head indicates the duration of the note. Therefore, a half note will have more space than a quarter note. Space allotted for a note is relative and not mathematical. Notes of equal value are spaced the same distance apart.
Common Errors
Tempo marking not aligned with time signature.
Important heading (composer, instrument, etc.) omitted or not properly placed.
Dynamic marking to the left of the note it affects instead of being under it.
Slurs on the wrong side of the note head.
Slurs between the note head and the articulation.
Incorrect stem direction.
Crescendo and Diminuendo marks that do not start or stop where the actual crescendo or diminuendo starts or stops.
Incorrect spelling.
Too many measures per line.
Use of a half rest in three-four time.
Very important symbol like a repeat sign or coda sign omitted.
A comprehensive article about music notation is beyond the scope of this site. I would like to recommend the following books as resource material for those of you who would like to know more.
Music Notation by Gardner Read, published by Taplinger Publishing Company, N.Y., 1969.
The Art of Music Engraving & Processing by Ted Ross, published by Charles H. Hansen Music and Books, Inc., Miami Beach, Florida, 1970.