From Stansted to Euston (for Novotel)
EITHER: Bus A6 from Stansted Airport to Golders Green Station. Then Norrthern Line Tube (any southbound train) to Euston.
OR: Bus A6 from Stansted Airport to Baker Street. Then walk about 1.5km directly East along main Marylebone Road/Euston Road road to hotel
OR: (more expensive but possibly quicker) Stansted Express train to Liverpool Street, then Circle Line Tube to Euston Square
http://www.londontoolkit.com/travel/stansted_airbus.htm