Most of your problems are related to people discovering the body. Social tactics are another core part of playing impostor but that’s so broad I can’t address it here.
The easiest step you could take to reduce the frequency the corpses you make are discovered is to use your tools of sabotage. As an impostor you have a variety of abilities that allow you to disrupt the game and restructure the priorities of the crewmates.
The simplest and one of the most effective tactics is to wait until you are alone with a crewmate, sabotage a crisis on the opposite side of the ship, and immediately kill the solo crewmate. The crisis will draw other crewmates to fix it, which brings them away from the body, allowing you to slip away and have plausible deniability. The best part? If the crewmates ignore the crisis and let the timer reach zero then. you win!
The second critical sabotage you can create is to kill the lights. This reduces the crewmate’s vision to about what is an arm’s reach away, anything outside of that length is obscured. While the lights are off you, as an impostor, retain full perception and can seek out and kill with a high level of impunity. Even in a crowded room you can still kill unseen if the lights are out.
The last sabotage you can inflict is locking doors to a hallway. This is still a powerful tool if used properly. The core use of locking a door is to briefly keep people out of a room, or to purposefully lock people in a room. Locking others out of a room allows you to kill and vent away while guaranteeing there are no witnesses. Likewise, trapping somebody in a room may give you enough time to finish your kill cool down and strike again before your quarry is able to escape. Both forms of door sabotage are situational, but in the right situations they can be used to great effect.
There are an endless supply of tips to maximize your killing potential when playing as impostor - but the best teacher is practice. As you play more rounds of Among Us you’ll learn through trial and error what tactics work best and what tactics get you caught. It’s not fun to be caught now but as you play more sessions your skill level will increase and you will become more lethal.
After a few tries I managed to do it, it's just pure luck to do it though.
For those of us wondering, you can still do tasks and win that way as crewmate, this will respawn all the dummies. (Although, a simpler way would be to just become Impostor again and respawn them.)
Best Answer
According to GameWith and Reddit, you can use the Q and R buttons to kill and report respectively. A user in the Reddit thread mentioned if either aren't working, then you are probably focused on a particular task. If so, simply press Esc