千万 (be sure to / whatever you do)

"Whatever you do, be sure to…"

• ten million千万qiān wàn = "be sure to / by all means" — an urgent plea.
• 千万别qiān wàn biéto arrive late迟到chí dào = "whatever you do, don't be late!"
• It's most common with don't别bié / don't不要bú yào (a strong warning).

ten million千万qiān wàn + (don't别bié / want / will / need要yào) + Verb

• ten million千万qiān wàn stresses how important the instruction is.

you你nǐbe sure千万qiān wàndon't别biébe late迟到chí dào！

• 千万别qiān wàn biéto arrive late迟到chí dào = "be sure not to be late!"

Earnest, not casual

• ten million千万qiān wàn carries real urgency — you really mean it.

Recap

Read the full reference: HSK 4 grammar — Adverbs.