If something often happens, it happens many times or much of the time.
They often spent Christmas together.
他们经常一起过圣诞节。
That doesn't happen very often.
那不常发生。
You use how often to ask questions about frequency. You also use often in reported clauses and other statements to give information about the frequency of something.
How often do you brush your teeth?
你多久刷一次牙?
every so often
If something happens every so often, it happens regularly, but with fairly long intervals between each occasion.
She's going to come back every so often.
她偶尔会回来一下。
as often as not , more often than not
If you say that something happens as often as not, or more often than not, you mean that it happens fairly frequently, and that this can be considered as typical.
Yet, as often as not, they find themselves the target of persecution rather than praise.
然而,他们发现自己往往是被刁难而不是表扬。