The games that ended in round 1 were a complete failure of the investigators. How could the single cultist get their kills so quickly? It's simple... the investigators put themselves in a place too early where all/many players have to go through after them.
The cafeteria and the green room in particular are very dangerous.
So if I am the starting player and standing in green, 2-4 players will probably run through me and thus I am 1) 99% dead or 2) the cultist myself and thus get my necessary kills directly.
DON'T - DO - THAT!
Talk to each other, the last players in the round can go to these places in the first round, everyone else should use paths to be efficient. Don't give the cultist a free encounter. They will take advantage and they will end the game faster than you can pronounce Cthulhu.
Do not accept encounters that are not necessary. Should you notice that players actively have encounters even though it doesn't seem necessary or is still way too early in the game? Use the secret weapon... and claim that you are going to check if someone has been killed this turn. The camera in the red room is exactly for this purpose. Whether you go there when it's your turn is up to you, but just claiming it often leads to cultists not killing for fear of being caught. This means they have had a harmless encounter and you don't have a potential new dead player at the table.
If you encounter too many players, the chances of you being dead or mistaken for being a cultist increase. As an investigator, you don't want either, so just avoid it! Try to always meet the same players IF you can't avoid it. That way you can always say "Yes, I have an encounter now, but AGAIN with the same person. So if I am a cultist, I won't be able to kill anyone new."
Logic helps here, as in the Among Us video game you like to go through the map in familiar troops, although it is of course safest to play alone.
Instead of unlocking all rooms, try to focus on the rooms that were unlocked quickly. You don't need all the points, you won't get them anyway. So look at how many points you are missing and try to focus so that you get the points. Nevertheless, have Plan B rooms ready, which may be close but not yet finished. Who knows when the next -1 Sabotage card will disrupt your plans.
You're in round 6 and still no points? Don't worry, that's normal! You'll get a hell of a lot of points in rounds 7-10 and can usually end the game faster than in round 10. Put pressure on the cultists... an earlier end helps you, because the cultist loses time to make his killings.
If you don't actively work on the points, the cultist can relax and win without working... so that makes little sense. Even if the point victories only make up 20-25% of the games, it is ALWAYS possible, just hang on until rounds 8, 9 or 10.
Cultists will hunt you down, strike at the right moment and kill you. For example, through random encounters or triggered encounters. They will also sabotage rooms or focus on just one thing. It's important that you don't lose sight of either. You don't have time to counter-check every encounter three times, then you won't score any points. But just scoring points doesn't make much sense either, as you'll lose out on kills.
So keep your actions balanced.
Shifting too much weight to one side will cause you to fall over.
Unsafe Passages are your enemy. They start with 50% negative. So if you do nothing here, there is a good chance that 1-3 Cultist tokens will block rooms (or even worse, when the Fishman appears because there are no more Cultists to draw). So you're wasting actions here because you have to fight them all. As a good investigator, you need to know when it's a good idea to secure the pathways. This is best done quite early in the game, e.g. in rounds 1, 2 or 3. Clever cultists may work against you and also manipulate the corridors. This can give you an important clue. It is important that you try to achieve a 2:1 ratio, this will secure your actions in the long term and will not block the vote, the camera or the portal at crucial moments (as this is exactly where the cultist markers can appear).
Sometimes you realize that you can't reach your destination. This can happen to anyone, but you can often prevent it. Look at your route, see where you have to go next round. Sometimes it makes more sense to choose a certain color so that you have a more accessible destination the round after. Try to be effective and efficient. Cultists will sometimes be able to do "nothing important" anyway, but the important thing is... that you loyal investigators always make sure that you get closer to your goal.