Place an adverb of definite frequency at the end of a sentence.
Examples:
"I go skiing once a year."
"Jack has been to China twice."
"Lisa dusts the house weekly."
However, an adverb of definite frequency may occasionally be placed at the beginning of a sentence for stylistic or emphatic reasons. Remember to place a comma after the adverb when using this style.
Examples:
"Once a year, I go skiing."
"Twice, Jack has been to China."
"Weekly, Lisa dusts the house."
Position an adverb of indefinite frequency before the main verb in a sentence.
Examples:
"John always wins at bingo."
"Harry rarely orders pizza with anchovies."
"The girls normally do their homework before watching television."
Remember the one exception; when the main verb is a form of "to be," an adverb of indefinite frequency is placed after the verb.
Examples:
"They are never sad."
"Lions are always hungry."
"We were seldom happy about returning to work."
Insert an adverb of indefinite frequency between the auxiliary verb and the main verb when a sentence has more than one verb.
Examples:
"The boys will seldom brush their teeth when they are at camp."
"Drivers should constantly check their rear view mirrors."
When a sentence has two auxiliary verbs and a main verb, an adverb of indefinite frequency is placed between the two auxiliary verbs.
Examples:
"The teacher will always be praising her students."
"The computer could never have made an error."
Put the following adverbs at the beginning or end of a sentence for style variation: "frequently," "occasionally," "often," "sometimes" and "usually." (Unlike adverbs of definite frequency, do not use commas when adverbs of indefinite frequency begin a sentence.)
Examples:
"Occasionally he goes canoeing."
"Frequently they ride their bikes."
"I sing in the shower sometimes."
"The frog likes sitting on the lily pad usually."