My tactic, and everyone will find their own method, but this works for me, is to work on the flats to stay in a group but don't let your nose get out in front. Sit in the draft, and work hard enough to stay in that group. If you are feeling strong, and you think you can jump to the next group ahead, then give it a go, else just sit in. On any little incline (there are a few in London even on the 'flat' sections, then work hard to get over the top of these lumps and not lose your group, but then just sit in again.
When you get to the hills, just ignore everyone else. I used to try to race those around me, and this would end up with me going into the red and blowing up. As there is next to no draft benefit on a climb I just ignore what others are doing; settle into a rhythm you're comfortable with and just turn the pedals. Ignore anyone overtaking you ... if you chase, you will probably blow up.
Like I say, works for me now but may not work for others