Now, imagine that you're reborn into a family of cavemen, around the time of late ice age, during the stone age. Around the time when you're 12 (you don't know you're 12, you just assume you're 12 because of your size), your tribe suffered horrendous defeat at the hand of a rival tribe. You lost all your food supply, half your people are killed or taken away, your father is dead and the only friendly tribe wants you gone from the area (after giving you some meat for the journey). You did not carry over any tools from the modern age or have any magic power. But you were from the modern age, and you knew things they didn't. For example, you knew that those tall grasses were actually ancient wheat and could easily sustain your small group of people. You also knew that those pretty grass you find throughout your nomadic life was actually flax, which you could use to clothe your people. The problem is, they won't follow you, because you're pretty much the smallest 'adult' in the group and you will never beat any of those bigger cave men. But you need to take over the tribe and you need to call all the shots because you know how to build fortifications, bricks and farming, all of which are skills that has little value to them because they're hunter-gatherer nomads. So what would you do in order to take over the tribe in order to bring civilization to these smelly cave men? How would you impress them and make them accept you as their king?
I'd probably not go straight to farming since that's pretty hard to figure out from scratch, and at the very least it's much easier to go find food than to grow it by hand. Honestly my move would probably depend heavily on the location I end up, with factors such as climate and local resources to keep in mind. If possible I'd like to jump right to the iron age since I at least know how to process ore from scratch, then I give could weapons to my tribe in exchange for food. Probably though, the best bet would be to somehow convince the other tribesmen that I'm somehow a divine being who remembers my previous life in the world of the gods, and make myself their religious leader. The trick really is to not try and change their whole way of life right away, since pretty much every group would be resistant to losing their whole way of life.
As you have stated, fortification, bricks, and farming will do nothing to impress a tribe of hunter-gatherers. If the transition to an agrarian society has yet to happen, none of them matter. The best you could do is try to leave a record of this knowledge for future generations. Unless you just so happen to be sitting on a piece of fertile land with great hunting spots and manage to convince people to stay there, chances are that you won't ever see the day such a civilization begins. The best way to impress a tribe of hunter-gatherers is to be the best hunter-gatherer. Hunt the most animals. Hunt the biggest animals. Gather the most plants and berries. What you currently need to know how to do is not how to build a brick house but how to craft the best weapons and how to hunt for prey.
I'm not sure what kind of answer you are looking for. However, in those times, the strongest ruled. If you are weak, find a way to control and use the strongest person in your tribe. If you have strength, others will have no other choice but to follow you. If some rebel against your leadership, find a suitable punishment, not debilitating or death because human resources are scarce. Well, unless the rebel was more troublesome than useful, then removing them would be the best course of action. In order to become "king" you need power, the first action that should be taken is to secure strength. You may be the wisest person in your tribe, but if you are not respected by someone who has strength, it doesn't matter. Those are my thoughts if you are dead set on improving your current tribe and decide against running off to live a beautiful quiet life.
That's what Ai-chan thought too. If you can't fight another caveman in a duel, then it has to be through a contest. Such as by deciding who can hunt the most animals first. Unfortunately, animals is also the reason why the friendly tribe chased them away. There wasn't enough animals to hunt in the area and the food they gave were barely enough for them to leave the area. The problem is, if they choose a bad direction, they will just die of starvation. The reason why you want to take over the tribe is because you knew there was a fertile land in one of the areas your tribe hunted before in the past and you've already hidden some wheat berries in a cave that you sealed with fired clay. The river would also be filled with fish at this time of the year. But even if you can explain this to them, it is unlikely that they will understand what you're trying to tell them. After all, the only reason you knew it's the season for river fish is because you've been keeping your own calendar so you know what season it is.
Shinier sticks! But it all honesty, like all things it is all about factions. You aren't the only 12 year old right? So the first thing one should do is conquer those your own age and below. Below is the easier prey. And the quickest way to do that is through their stomachs. While pulling out technology is pretty hard, things like traps are something that can be used to gather food. You use that to bait in the other children, especially the ones younger than you (those your own age may contend with you so you gotta be a bit careful). Once they see you able to gather food, they will listen to you and you can use them to distribute tasks. You probably also want to teach the younger children how to read and write on the side, plus modern self defense (you gotta make some long term investments). Given enough time, the children will boast to the adults about this and that. Now the question comes down to how the adult factions are distributed. If your parents are at the bottom of the hierarchy, you probably want to approach the old "wise" people and join their faction. If you are high, then even if it is more difficult, you should stand out in strength so that they see you as a perspective leader. And bribe the adults little by little in the form of presents.
This is where the rule "might makes right" makes its appearance, where you channel your inner Dwayne "The Rock" Johnson and triple-suplex-power-bomb-ultra-EX anyone who wants to be chief into the bedrock.
Welp, making fire & cooking w/ it were the first things came to my mind Depends on how well the "tech tree" developed, making rudimentary stone age weapons or upgrade to bronze age. Else, simple traps for hunting (more food = more respect)
Nooooo . . . . I don't want to travel back to that boring and uncivilised time My idea is WAKE UP IT'S A NIGHTMAREEEEEE But if i got in this situation, my thinking is 1. to survive long enough, don't get sick. 2. to brainwash people with similar age of mine or younger, i mean educate. 3. Make people believe you. However it is. It's first important step. 4. I don't know, I don't even think i can survive
Taking a page out from Chronicles of Primordial Wars, one could try fishing, assuming we do find a place to stay and it's next to a river with fish living in them. I don't think cavemen had thought of catching fish with a lure yet, and can probably only think of harpooning them, so catching food without spending too much energy would probably give you some, er, "street cred" in cavemen terms(?).