Kings Cross. Head east to Angel. Third exit at Angel will get you down St Paul's. Straight on to Old Street, third exit of roundabout south to Moorgate. At Moorgate turn left for Liverpool Street. South from Liverppol street gets you to Monumrnt and London Bridge.
West to Euston. British library between Kings Cross and Euston. South at Euston to Russel Square turn West for Birish Museum. South from British Museum is Oxford Street continue south west to Leicester Square, continue SW to Charing Cross, either west down mall to Buckingham Palace, or continue to House of Parliament or horse guards parade. Head west from Leicester Square for Piccadilly Circus
Cross over river from Houses of Parkiment and turn east for millennium wheel, Shard, Tower Bridge, HMS Belfast etc. on to Millenium Dome and Greenwich park etc.
Just look at a map beforehand, print it out and use highlighter pen for main landmarks you want to see. TFL also publish free cycle maps you can order in advance I have a few of those maps from my early ventures.
I generally carry a silva type compass and box my route by the main artery roads even a large scale map will show.