Which channels to listen to on liveatc concerning arriving flights?
If you want arrivals the relevant feeds on live ATC are:


NY app (CAMRN)
NY app (ROBER)
NY app (FINAL)
KJFK Tower
KJFK Tower #2
KJFK Tower 119.1
KJFK Tower 123.9


CAMRN will receive approaches from the south and ROBER will receive approaches from the east. They will then pass planes to final to be lined up to the runways. Final will then pass planes to the appropriate tower frequencies, depending on which runway they are assigned. There are two separate tower frequencies of which there are two separate feeds. Items 4 and 5 are both frequencies combined (usually one in the left ear and one in the right) from the two different frequencies. The feeds are done by volunteers so there's no way to know their location. I haven't listened to KJFK so one feed might be better to hear planes from different directions. Feed #1 includes the TCA. I find it daunting to hear two feeds at once so I would recommend using either 6 or 7. 

To be honest, unless there's something unusual going on, tower feeds are pretty boring. By the time they get to tower freq they are done maneuvering and are established on final. All tower does is clears them to land and and gives them exit instructions. If you are watching FR24 the approach feeds are more interesting. 

Another interesting approach to watch, at least for me, is KMEM between about 2230 and 2330 Central time when all the FedEx flights are coming in to the hub. Gives you a good idea of the flow of ATC.

As Dave mentioned in comments, none of the UK airports will be on LiveATC for legal reasons.