The first thing to get clear here is that Victoria Bus Station and Victoria Coach Station are two different places.
Victoria Bus Station is used by London Transport buses and is immediately outside Victoria Rail (&Tube) Station.
Victoria Coach Station is used by National Express and other long-distance coach services. It's � mile away from Victoria Rail (& Tube) station. (Just to confuse matters further, Green Line services have got their own terminal at Victoria, which is midway between the Coach Station and the Bus Station!).
First, get yourself to Victoria Rail Station. If you're arriving at Victoria Bus Station, you're already there. If you're arriving at Victoria Coach Station (or the Green Line terminal), simply walk along Victoria Palace Road until you get there. (It's signposted).
Follow the signs for the Circle Line (Westbound). Take a train, on that line, for 7 stops, to Paddington.
Chris