On the train
Being able to take your bike on the train is really important for intermodality. But there are limitations (moving within the stations and occupying space in the carriages) which have been overcome as best as possible. The main thing to bear in mind is not to take up the space reserved for people with reduced mobility or block the corridors and doors.
Each operator has a different policy on carrying bikes. In the rush hour bicycles can often be a nuisance and even a danger to other passengers since they take up a lot of space and there are not areas especially reserved for them. Also, sometimes the best place to put them coincides or is close to spaces reserved for wheelchairs or pushchairs.