This is a timeline of the 2008 Mumbai attacks.
In October, US intelligence agencies warned Ratan Tata, the chairman of the company that owned the hotel (Taj Hotels), that there would be a terrorist attack on the Taj Mahal Palace Hotel. Security was increased, but was removed soon after.
On 18 November, Indian intelligence agencies intercepted a satellite phone call to a leader of Lashkar-e-Taiba terrorist organization, which revealed plans for a sea borne attack.
Sources: NDTV, Evening Standard, and BBC