Keep Calm. The most important thing when dealing with an unpleasant or noisy neighbour is to always stay calm. Take a deep breath and think before you speak. Calming down will also help you understand if the noise simply annoys you or if it is actually in violation of the particular noise regulations in your building.
Communicate. The key to any problem is clear and concise communication. Knock on your neighbour's door and politely explain your problem to them. It's possible that they are not aware of how noisy they are being, are genuinely sorry and will make sure to lower the volume.
Get Out There. This is definitely not a long-term solution, but if there is a particular time you know your neighbour is noisy or having a party, use this as an opportunity to get out of the house! Go see a movie, work at a coffee shop or take a walk in the park.
Be Sweet. Literally! Bring some sweets or baked goods with you to lighten the mood and show that you are not angry, but would like to address a topic.
Pick Your Battles. There may be several annoying factors that you are experiencing with a particular neighbour. Sometimes it is important to really think about the problem and reflect on whether or not this is something worth complaining about or confronting them over.
Leave A Note. Not everyone is comfortable with confrontation. If it makes you feel more at ease, start your interaction by leaving a note. You can also add some humour to your message to make it friendlier.
Talk To Your Landlord. If all else fails, tell your landlord about the situation at hand and leave it to them!