Pick the instruments used in the score. If, for instance, your score includes seven parts, put seven lines in a bracket (one line of each part, playing together) called a system. The score order of instruments follows: woodwinds, french horns, brass, percussion, and strings. The score order means that the woodwinds, such as the piccolo, must appear on the top line in a score, while a stringed instrument, such as the contrabass, appears at the bottom. Write the clef of each instrument in its corresponding line, along with noting each instrument to the left of each line. Understanding the capabilities of each instrument requires much careful study for maximizing the potential of each instrument in the final product.
Choose the key and time signatures and write them into each line. For example, the key of D Major contains two sharps, F# and C#, so write the sharp symbols (#) after the clef symbol in the place of F or C to indicate that those notes are played sharp unless otherwise noted. Next write the time signature, which is a number indicating the number of beats per measure, with the note value worth one beat below it, such as 4/4 or common time.
Begin notating. If you are not using composition software, follow a few guidelines for an accurate score. When notating longer note values (such as quarter, half, and whole notes), leave ample space between the notes because you will align the tempo up and down the score. For example, if you write a brass part with four quarter notes in a measure (in 4/4 time) while the violin plays sixteen 16th notes, leave enough space between quarter notes to allow four notes written beneath it easily. Using a ruler to see the beats literally line up is advised for a clean, understandable score; as in the previous example, the first 16th note lines up with the first quarter, and the fifth 16th note lines up with the second.
Add other markings, such as tempo and dynamics. Tempo markings like "presto" indicate playing at a fast speed (tempo) during performance. Classical composers/arrangers usually learn the Italian terminology for formality's sake--the "universal language" of classical music across countries--but on many occasions use English. Other articulation notes might include words like "pesante" above the music, meaning "heavy," to give players an idea for the feel of the music; a dot above a note indicates "staccato," or a short note, while a line above a note indicates "legato," or a long note played out smoothly without a space. "Dynamics" pertain to the loudness or softness of the music, marked beneath each line always with "F," (meaning "Forte"--loud) or "P," ("Piano"--soft) or multiple marks to emphasize how loud or soft. The timing of this step depends on your preference, but focusing on the details tends to come after the notation and may make the process easier. Depending on the piece of music, you may find a need to switch time and key signatures during the composition.