I used to live on the corner of Streatham High Rd/Greyhound Ln. Going into London I'd head up the A23, then turn left down Drewstead Rd just before Streatham Hill Stn, along Sternhold Ave, round the common to Emmanuel Rd and then Cavendish Rd.
Coming back out of London I'd follow the LCN route (I think it's route 5, this was in 2006 so my memory/the route may have changed): Garrads road, across the junction and over the pavement to Riggindale Rd and down to the end of Conyer's Rd, down the alley under the railway onto Estreham Road.