Often, people will have trouble making themselves stand out form the crowd. For some people, they can be a bit nervous about voicing their own opinion; maybe they are worried about being wrong or be laughed at. So, trying to stand up for themselves, and really assert themselves can be a problem for some people.
It has been popular in recent years for schools to focus on building up the self-esteem of children. This can make many of them very assertive. Yet, often they are too assertive and they end up offending people. So, there is a fine line to walk when you want to assert yourself without coming across as mean or nasty.
Step one in doing that is to stop and think before you speak. Ask yourself, what is the point I'm trying to make. If you disagree with someone over a political view, the issue of Global Warming, or something else, making your view point known is one thing, being mean, nasty and/or insulting is quite another. Do that, and you will more than likely lose friends and not influence people in a positive way.
Next, there is the manner in which you express your view. You must not yell or shout it out. Do not interrupt other people when they are speaking. There is the old saying about doing unto others as you would have them do unto you. You definitely wouldn't like people to interrupt you, yell at you, or belittle your opinion when you are having a chat. So, you should not do the same to them.
Another point to consider - staying on the subject. If you are talking about the upcoming Presidential election, then only talk about that. People will not like being around you if you are constantly changing the subject to suit your needs. In addition, if you are engaged in a debate, and the other person makes a good point, do not retaliate by then moving on to a totally unrelated subject.
There is also the matter of choosing the right time to be assertive. When you are out with friends and you are trying to decide which movie to go to, that is not the time to be so assertive as to demand that everyone see only the movie you want to see. Ironically, looking at the military is a good way of illustrating this point. Soldiers are given orders on a daily basis. Yet, there are times when they do not agree with those orders. Still, they follow them. But, there can be times when a soldier will be given an order and know that it is not right, that it should not be followed. That is when the solder must assert himself and refuse to obey. A good soldier is not merely a robot who blindly follows orders; a good soldier is aware that there may come a day when he will have to disobey. When that day comes, he will have to have a reason for it. Well, the same is true of being assertive. It is the right thing to do; so long as you do it at the right time.
Finally, when making a point - make it and move on. If you just keep repeating the same point over and over, hoping that eventually people will accept, you are not going to win people over to your way of thinking. If you keep harping on the same thing, you are going to start sounding like some sort of conspiracy nut. That is not how you get people to listen to you. One of the key aspects of being assertive is also being realistic; understand that not every person you speak to is going to agree with you, no matter hoe persuasive you are.