Have you got any tips on four-part writing (preferably on a grade 5 music theory level)?

1) This could be interesting:
"GARRITAN INTERACTIVE
PRINCIPLES OF ORCHESTRATION
by Nikolay Rimsky-Korsakov"
http://www.northernsounds.com/forum/showthread.php?t=48158


2) "Four-part writing
Four part chorale writing is used to teach and analyze the basic conventions of Common-Practice Period music. In the German musicology tradition referred to as functional harmony. Johann Sebastian Bach's four voice chorales written for liturgial purposes serve as a model for students. These chorales exhibit a fusion of linear and vertical thinking. In analysis, the harmonic function and rhythm are analyzed as well as the shape and implications of each of the four lines. Students are then instructed to compose chorales, often using given melodies (as Bach would have done), over a given bass line, or to compose within a chord progression, following rules of voice leading. Though traditionally conceived as a vocal exercise for Soprano, Alto, Tenor, and Bass, other common four-part writings could consist of a brass quartet (two Trumpets, French Horn, and Trombone) or a string quartet (including violin I, violin II, viola and cello).
There are seven chords used in four-part writing that are based upon each note of the scale. The chords are usually given Roman Numerals I, II, III, IV, V, VI and VII to refer to triadic (three-note) chords which are based upon each successive note of the major or minor scale which the piece is in. Chords may be analyzed in two ways. Case-sensitive harmonic analysis would state that major-mode chords (I, IV, V7, etc.), including augmented (for example, VII+), would be notated with upper-case Roman numerals, and minor-mode chords, including diminished (ii, iii, vi, and the diminished vii chord, viio), would be notated with lower-case Roman numerals. Schenkerian harmonic analysis, patterned after the theories of Heinrich Schenker, would state that the mode does not matter in the final analysis, and thus all harmonies are notated in upper-case.
The skill in harmonising a Bach chorale lies in being able to begin a phrase in one key and to modulate to another key either at the end of the first phrase, the beginning of the next one, or perhaps by the end of the second phrase. Each chorale often has the ability to modulate to various tonally related areas: the relative major (III) or minor (vi), the Dominant (V) or its relative minor (iii), the Sub-Dominant (IV) or its relative minor (ii). Other chromatic chords may be used, like the diminished seventh (made up of minor thirds piled on top of each other) or the Secondary dominant (the Dominant's Dominant — a kind of major version of chord II). Certain standard cadences are observed, most notably IIb7 – V7 – I. The standard collection of J. S. Bach's chorales were edited by Albert Riemenschneider and this collection is readily available, e.g. here; the student is greatly rewarded by playing them at the piano, singing the lines by themselves, singing them in groups, analyzing them by writing the Key and the Chords employed and by taking the melody and bass line from any chorale and trying to fill in the inner alto and tenor parts. Once this has been accomplished the student can then begin to complete their own bass lines —whilst carefully watching for modulations— and then they can fill in the inner alto and tenor parts. Parallel octave and fifth motion is forbidden, and this often proves to be the pons asinorum of the average music student.
Source and further information:
http://en.wikipedia.org/wiki/Music_theory#Four-part_writing


3) "USE PROPER NOTATION.
Notate the soprano on the treble clef staff with stems up, the alto on the treble clef
staff with stems down, the tenor on the bass clef staff with stems up, and the
bass on the bass clef staff with stems down."

"Chords may be in open or close spacing. Chords are in open spacing when you
can put another chord tone in between the soprano (S) and alto(A) and/or
between the A and tenor (T) voices. Chords are in close spacing when no
chord tone can be placed between the SA or AT voices."

"• MAINTAIN 4 DISTINCT VOICES; MAINTAIN THE INDIVIDUALITY OF THE VOICES.
Keep the voices in their proper ranges.
Soprano Alto Tenor Bass
The maximum distance between SA and AT is a P8; between TB, the maximum
distance is 2 P8s.

Do not cross voices (in the same chord). Do not overlap voices (between two
adjacent chords).

Use contrary or oblique motion to the bass more frequently than similar motion.
Use parallel motion only when necessary.

* Contrary motion -- voices move in opposite directions.
* Oblique motion -- one voice remains on the same note while the other
voice moves.
* Similar motion -- voices move in the same direction by different
intervals.
* Parallel motion -- voices move in the same direction by the same
interval.

NEVER write parallel P1, P5 or P8."
Source and further information:
http://web.utk.edu/~mtheory/documents/Murphy_110_PartWritingRules.pdf