1. The train schedules will change in summer. You can expect busier train lines and it might be more challenging to find seat reservations. Usually, you do not need seat reservations but do research beforehand if you have your mindset on specific destinations. You can check your route and the seat reservation policy here.
2. If you want to bring your bicycle to combine a rail adventure with bikepacking, then you must look into bike tickets. You might need a bike ticket to bring bicycle on the train.
3. How far do you want to go and how much time do you want to spend traveling versus being in destinations. Although the Interrail passes are usually valid for two to four weeks, you will have fewer so-called travel days (the days when you can travel by trains in the regions that your Interrail card is valid).
4. Just like trains are busier in the summer season, hotels can be fully booked. So it might be an idea to arrange your hotel bookings well in advance. Hint! If you decide to travel the lesser-traveled areas and closer to nature, chances are you can use some more flexibility. But if you want to do city-hopping to places such as Berlin, Barcelona, or Paris, then you should research hotel room availability beforehand.
5. To avoid too much stress in the heat of the summer season, alternate your travel itinerary between cities, nature, and smaller villages. For example, if you are planning on going on an Interrail trip in Western or Central Europe, then you can easily include the Alps, a few larger capitals, and smaller villages along the rail routes.