What the Muqtadi should do and should nat do after the Imam has completed

1. If the Imaam performs the Salaam before the Muqtadi can complete the Tashahud, then the Muqtadi should complete it.

2. However, if the Imaam raised his head before the Muqtadi can complete reciting 3 Tasbihs of ruku or Sajdah, the Muqtadi should follow the Imaam.

3. If the Imaam performs an extra Sajdah or stands up by mistake after the final Qaidah, the Muqtadi will not follow suit and when the Imaam thereafter consolidates the extra Rakaat by making a Sajdah the Muqtadi should make Salaam on his own.

4. If the Imaam stands up before the final Qaidah, by mistake the Muqtadi should wait for him.

5. If the Muqtadi makes Salaam before the Imaam consolidates the Rakaat by making Sajdah, then the Fardh Salaat of the Muqtadi is nullified.

6. It is Makrooh for the Muqtadi to make Salaam after the Imam’s Tashahud, and before the Imaam’s Salaam.

 Source: Taleem ud Deen by Shaykh Mufti Afzal Hoosen Elias.