>>> Buenchico is it really that difficult to negotiate?
As Donny48 says, it's nowhere near as bad as it used to be. In the days when there were toll booths, traffic crossing the bridge (in 4 lanes) had to divide up into about a dozen queues for the toll lanes, with the right-hand lanes being unmanned. (You had to have the right money, which you simply threw into a receptacle to open the barrier). So people who suddenly realised that they'd not get change were fighting to get across from the right-hand lanes to the left-hand ones, while other people were changing lanes to seek the shortest queues. On exiting the barriers the dozen-or-so lanes created by by the toll barriers then had to merge back into 4 lanes. (That was bad enough but people who'd used the unmanned barriers on the right, and who needed to take the first exit off the motorway, were fighting to get across to the left). It could get a bit chaotic at times!
These days everything flows fairly freely over the bridge. Simply get in a lane and stay in it. (That's exactly what the signs say you should do but you still need to watch out for idiots who keep changing lanes). If you'll be leaving the M25 shortly after the crossing, choose a lane towards the left, so that you'll be in the right place. (For the A2/M2, for Ebbsfleet International and Canterbury, make sure that you're in lane 2 as soon as possible after the crossing. For the M20, for Eurotunnel and Dover, lane 2 or 3 is probably the best one to seek out after crossing the bridge).
Going northbound is also far less hassle than it used to be. The main thing to be aware of is that there are actually TWO tunnels (which, in the days before the bridge was built, used to carry traffic in each direction). So, as you approach the crossing, look well ahead to see whether the lane you're in is going into the left tunnel or the right one. (Also be aware that there are two lanes in each tunnel, with no lane changing permitted. So the motorway lane you're in might, for example, be feeding into the right-hand lane of the tunnel on the left - don't try to get across to the left-hand lane).
It's all fairly straightforward but I still recommend giving a firm instruction to anyone who's in the car with you: "Shut up while I concentrate!"
;-)