Prevent problems first:   The best way to eliminate problems is to avoid them.   My first piece of advice is to understand exactly what you are purchasing, what's included, what are the extra charges, and what are the total costs.  Do the research on hotels, restaurants, airlines, tours by looking at their websites.  I also use TripAdvisor.com as a resource.

Here are some tips for getting what you want:

Screaming doesn't help.  In fact, it will probably hurt your case.   When you scream at people, they hear you screaming, they don't hear what your issue is.   My advice is to try to get on their side to solve the problem.   For instance, if I got a room that was totally inadequate, I would approach the desk clerk with some like, "Hello, I hope you can help me solve a problem.   My room is very noisy and I just can't get any sleep.....I am sure you know how bad that can be".

Be clear with what the problem is.   I see people go to an airline, tour guide, hotel and say "This is ridiculous, I have never seen a (hotel, airline, tour) run as poorly as this".  Instead say, "my bags are lost" or "this is not what I ordered for dinner" for example.

Know How You Want the Problem Resolved.   Don't wait for the person who you are complaining to for a solution.   They probably don't know what you want either.    If you are clear in what you want, you are helping that person solve your problem.  Say something like "I need another room",  "I don't want to pay for this because it is not what I ordered", or "I would like the bill reduced by 75 euros".  For me, this is the most important tip.

Understand Your Limitations:  If the hotel is full, you are not going to get another room.  If the airline is not required to give you a refund, don't expect it.