The way that has served me well is this. Come up the M4 and stay on it when it becomes the A4 until the signposts show exit for Shepherd's Bush (before the Hammersmith floyover). Keep to the left lane after you turn off, and after a few sets of lights and 2 successive rounds of round-abouts where you keep aiming for Shepherds Bush. Hopefully, you find yourself on Shepherd's Bush Road which you follow up to the Green, when you keep to the right and turn right around the Green. You go past the Empire on your left so make sure you're turning right when you see it.
Follow past the shops to another big round-about and take the left just after the tube station, up the dual carriageway towards the Westway and the A40. You want the Eastbound carriageway so around another couple of round-abouts and you should find yourself heading up the Westway into Marylebone Road and then Euston Road. Now you just follow your nose for a few miles, go through Kings X and up the hill. Turn left by a hotel (can't remember the name now) at top of hill and follow road around to Islington High St. Road comes out opposite the tube and you have to turn left.
Turn left and drive up through 3 or 4 sets of lights, keeping on the right lane so that as you hit Islington Green, you take a right turn. This is onto Essex Road, which you drive the length of before turning right onto Balls Pond Road after a mile or two, when you see a church on the left. Then you simply follow your nose really, straight ahead and after driving thru Dalston and Hackney, you'll see signposts for Clapton.
I think it avoids all of the congestion charge zones and is reasonably quick and straighforward when i've done it that way. I have come back thru Picadilly on a couple of times and it really is worth avoiding imo/e.