Easy Peasy. it's about 2 miles.
North from Victoria up Grosvenor Place (Past Wellington Arch, meet of FNRttC & The CC Sunday Morning Meet)
Now you can either go through Hyde Park (that will be shut at night) or up Park Lane (right at Hyde Park Corner, then left.)
Up Park Lane then around Marble Arch and onto the Edgware Road, turn left into Pread Street and Paddington Station is on your right.
It's a very busy route to cycle, but if you are an experienced cyclist then it will be no problem.
edit. just remembered part of Praed St is one way so you would need to turn left at Sussex Gardens then right into Norfolk place, left into Praed Street