How can I stop making assumptions?

Try to imagine what that person is going through. Other people might have the same problems as you and you have to be aware of that.

Everyone is at a different point in their life. Emotional stability is not line it is more of a bar graph. Some days you will be better than others, that is just life. Very few things in life will be game changers. It is important to ask yourself if it will matter a year from now. Most people do not set out to make you feel bad. Many people are simply just focused on their own problems, and don't stop to think about others.

When it comes down to it, assumptions are caused by a lack of communication. It can be difficult to gather the courage to ask questions but if you practice at it, you'll surely notice it becomes easier. The best thing you can do is practice talking with people and asking them questions. If you can't do that, try your best to let go of whatever assumptions you've developed. Just acknowledge them, then understand that you can't possibly know for sure, and forget about it. Don't let it trouble you until it comes up again, and then do your best to politely ask questions or think critically about why exactly you developed a particular assumption in the first place

well in my opinion you can change the word assumption to guess and opinion, that way you won't be assuming but will be guessing. But if you wanna do that too, I believe controlling your thoughts by like using meditation.

You need to understand that you don't know what persons story. You cannot judge till you know. There is always a reason someone is who they are.

by looking at facts and looking objectively at situations and observe a lot whats happening around you. not assume something, also you can ask, and check

Stick to what is happening in the moment. Don't try to predict anything and be clear about the facts.

stop thinking that there is reason/s behind everything "don't over psychologising" in our terms of words

Once you realise that you can never really know what people are thinking or why they have chosen to behave in a certain way, you can assure yourself that social pressures, judgment, embarrassment and shyness all play a part in how a person behaves. If you percieve someone's behaviour in a certain way, bear in mind that sometimes it is hard to tell why somebody behaved in a certain way or took a certain course of action. Maybe your own judgment is colouring your idea of why someone did a particular thing.

By being in the here and now. Challenging ourselves with questions, asking ourselves for evidences, doing self-reflection really helps.