How to express yourself as an introvert.

Introverts are not loud mouth. A lot of them finds it hard to express themselves, and even if they do, they get shunned or talked over. This affects a lot of introverts because communication is key in everything. We accept foods we did not order, contribute less in positive discussions, buy things of short quality, get cheated etc.

THIS HAS TO STOP.
Yes! We are introverted but not fools. You must express yourself to get exactly what you want. So for instance when you try to contribute in a gathering and a loud dude tries to talk over you :
Keep talking, slowly, even if the extrovert keeps talking it shows you are the more confident one, not trying to impose your opinion with force.
If a waiter brings the wrong order ; this is not what I asked for. Remember it’s your money, stop thinking you are offending someone and get the best for yourself.

If you are in a relationship as a introvert, let your partner know your dos and don’ts. Do not accept bullshit or get guilt trip or else you will regret it. This will save you from an abusive relationship. Remember that reaction, or disdainful look is for the moment.
Finally, PRACTICE. I am also like you, but have been practicing and getting better this is what I want for you too. Get out of your imagination and do it.