Parties, pets, pools, playsets and trampolines; what do all of these have in common? They create noise!
If you are designing a layout for your new home, you must always keep in mind that you need to consider the needs of the people who live around you. You can do this by designing your backyard so that the focus of the outdoor entertainment is away from the neighbouring party. Doing so will help alleviate some of the impact that the noise will have on your neighbours.
Assigning a play area directly adjacent to your neighbour's property is a terrible idea and should be avoided as much as possible. If you are an extremely quiet family with quiet children then you may get away with doing this and not cause any tension between yourself and the neighbours, but do be realistic -- kids will make noise as well as whatever equipment or toys they may be using.
To protect your neighbours' properties, you may want to consider a trampoline anchor kit. Anchor kits prevent trampolines from becoming airborne in stormy weather. Left untethered, trampolines may become lifted by the wind and may cause severe damage to neighbouring areas.
Be nice to your neighbours, and always be considerate!
If it's your neighbour with the trampoline, then you may want to approach them directly. It's always easier and faster to speak to your neighbour yourself. Perhaps they're not even aware of the problem, and will happily rectify the situation themselves.
If they refuse and you can't find a compromise, it may be time to complain about your neighbour's trampoline to the appropriate authorities. The body corporate or local council may be able to resolve the problem if your complaint is launched in the appropriate manner.