常常(cháng cháng) - often, frequently in Mandarin

常常 (cháng cháng) means often, and it goes before the verb, never after it: 他常常迟到, not 他迟到常常. That position is the single most useful thing to fix in your head, because English lets "often" drift about the sentence and Chinese does not.

The negative is the trap. 不常常 is wrong; you say 不常 (bù cháng) using the single character, or 很少 (hěn shǎo, rarely). Reduplicated adverbs generally refuse 不 in front of them, and this is the one learners hit first.

Against its near neighbours: 经常 (jīng cháng) is a shade more formal and works better in writing, 总是 (zǒng shì) is always, and 通常 (tōng cháng) is usually in the sense of as a rule. 常常 is the plain spoken option.