Excerpt

A/AN
	There is confusion as to which is used before certain words. Here is the basic rule: before words beginning with a consonant use a; words beginning with the five vowels a, e, i, o and u, use an. If the beginning of the word sounds like a vowel, use an (hour, honor, honest), If u has a "yew" sound, use a (a useful tool). Also, use an before the following alphabet letters standing alone: F, H, L, M, N, R, S and X. That's because these letters, spoken aloud, sound like "ef," "el," etc. (example: "an FBI agent.") The h is spoken as "aytch." Common error: an historical event; make that, a historical event.
A.M./P.M.
	There's obviously nothing jarring about these letters. What is to be avoided is, as always, redundancy. (incorrect) three A.M. in the morning (correct) three A.M. (correct) three in the morning The same is true for its P.M. sister phrase.
ABILITY
	You (if you want to sound correct) have ability at drawing but ability with tools.
ACCEDE/EXCEED
	Care is needed in regard to the first syllable of each. The former word means to agree to, to give in. The latter word means to surpass, to go beyond.
ACCESS
	This noun means a way in or out (access to the fort was by way of a drawbridge). The word is also a verb (to access the data or information). A problem arises when the verb use is extended beyond data or other computational usage (to access the valve in the cabinet beneath the sink). The extending of the verb use if meant to sound high-tech and impressive, but usually grates on the ear. Try: to reach or use the valve... Incidentally, it is useful to be sure to pronounce the first syllable "acc", not "ess" (as in excess).