Propaganda has always been there, but propaganda taylored in a scientific manner, propaganda that lies on multiple sources to confirm each other and appear credible, propaganda that exploits all the possible weaknesses of human psychology with the help of expert in the fields, that is something new that was created in the United States in the first half of the 20th century. That is the most powerful propaganda and to detect it, disentangle it from the facts requires a lot of attention, good memory and a strongly critical attitude towards everything that is being told or written.
Since the new propaganda was born a lot of people began to worry about their power, in order to allay the fears one of the most famous gurus of the new era wrote few books on the subject trying to mimimise the dangers of the new science. I am talking about Edward Bernays and his books even though they are permeated by an optimist tone bordering the wishful thinking can still teach a few things about the effort, the scientific approach and the study behind it:
Beside that there is a lot more to watch out for. Propaganda is not just about telling, lies often persuasion is achieved by exploiting the most common weakness in human thinking, that is, judging by association in order to reduce the time and the effort that would be required by a proper judgement. You should always wonder if an association between a known stereotype with marked characteristics and an argument or a cause makes sense. Even more wary you should be when a person known to be hated by people of a certain group marries a cause which those people might embrace. The most famous example is Trump who often does not talk in favour of a specific cause to help it, but to taint it, in such case you cannot differentiate the news from the propaganda, because the action making the news is the propaganda itself.
One more point. As I said above also a good memory is important because propaganda needs to rewrite the history every now and then in order to keep the image of the present more credible. A good example is what happened in Myanmar. After the 2020 elections which saw a landslide victory of the ruling party protests broke out in the entire country. After a long period of protests the military junta overthrew the government and started a heavy handed repression. After an initial wave of news for a while there was little information in order to let people forget what was happening there, now a new narrative is emerging. It tells that the military junta staged a coup against a popular government, it paints an image of a junta hated by the people against an overthrown government supported by the people, while in reality protests were going on against both the junta and the overthrown government. In this case only who still has in mind the correct temporal sequence of events can see the propaganda.
Another thing, you should pay attention to, is silence. In a media that is supposed to tell the voices of thousands of people counting journalists, politicians and experts you would expect to hear a lot of different opinions, if they all agree there is something strange, if they all seem to forget/overlook the same issue it is even more strange. When absolutely nobody wants to talk about a specific issue that is really the moment you should wonder "why?".