Spelling Rule #1
The letter c, in French, sounds like a hard k unless it is followed by the letters e or i or is softened by a cedilla (ç).

Examples:
la cantine (hard "k")
ici (soft "sss")

Verbs that end in -cer change to ç when the letter c is not followed by e or i in the verb ending. The most common of these verbs are annoncer, avancer, commencer, effacer, lancer, menacer, placer, prononcer, remplacer, and renoncer.

Example:
je commence, tu commences, il commence, nous commençons, vous commencez, ils commencent

This change also affects the imperfect tense, so be alert.

Example:
je commençais, tu commençais, il commençait, nous commencions, vous commenciez, ils commençaient

For the nous and vous forms, the c is softened by the following letter i of the imperfect endings.

Spelling Rule #2
The letter g in French sounds like a hard g as in the English word "gate" (le garçon) unless it is followed by e or i. A softened g sounds like the j in je or the s of the English word "pleasure." Since there is already a tail on g and it would be hard to add a cedilla, we soften the g by inserting an e after it.

For example, the present participle of the verb changer is changeant.

For verbs that end in -ger, the letter e is inserted to soften the g when necessary. The most common -ger verbs are arranger, ranger, changer, corriger, décourager, déranger, manger, nager, neiger, obliger, partager, plonger, songer, and voyager.

For example, the present tense of the verb nager goes like this: je nage, tu nages, il nage, nous nageons, vous nagez, ils nagent.

Again, it's the nous form of the present indicative that needs the e added. The imperfect forms will also be affected, as in je nageais, tu nageais, il nageait, nous nagions, vous nagiez, ils nageaient.

Spelling Rule #3
The letters i and y have the same pronunciation and a close relationship.

Verbs that end in -yer change the y to i in all but the nous and vous forms; y changes to i in all the mute endings (-e, -es, -e, -ent). However, there is a special rule to remember with -ayer verbs. These verbs may change to i or they may keep the y for all forms. Both are correct.

Example:
The conjugation of payer is je paie / je paye; tu paies / tu payes; il paie / il paye; nous payons (no choice); vous payez (no choice) ils paient / ils payent

Common -yer verbs are balayer, employer, ennuyer, envoyer, essayer, essuyer, nettoyer, and payer.

Spelling Rule #4
Verbs with an acute accent in the next-to-last syllable of the infinitive need to change the acute accent to a grave accent in the silent-ending verb forms. (Nous and vous will keep the acute accent.)

The most common verbs in this category are céder, célébrer, compléter, considérer, espérer, exagérer, interpréter, posséder, précéder, préférer, protéger, répéter.

Example:
Je possède, tu possèdes, il possède, nous possédons, vous possédez, ils possèdent. Nous and vous keep the acute accent.

Spelling Rule #5:
Verbs with a silent e in the next-to-last syllable of the infinitive change to an è (sounds "eh").

Example:
je mène, tu mènes, il mène, nous menons, vous menez, ils mènent

Common verbs are acheter, achever, amener, élever, emmener, enlever, geler, lever, mener, peser, relever, se promener, promener, s'élever, s'acheter, se lever.

Spelling Rule #6:
Two special verbs with a mute e in the next-to-last syllable of the infinitive, as well as their close relatives (appeler, s'appeler; jeter, se jeter) double the consonant in place of using a grave accent.

Example:
je m'appelle, tu t'appelles, il s'appelle, nous nous appelons, vous vous appelez, ils s'appellent