to jump the gun: to start doing something too soon, ahead of the others
E.g. The assistant jumped the gun by hiring the new employee, before the approval of the manager.
The athletes had to start the race again because one of them jumped the gun.
to jump to conclusion: to judge a situation without having enough information about it, to make assumptions
E.g. When people saw Brad and Jenny together, they immediately jumped to conclusions and thought they were dating.
We should not jump into conclusions. We will look like fools if we turn out to be wrong.
to jump through (the) hoops: to go through many (bureaucratic) obstacles, to do anything to get the desired results or to please someone
E.g. Jenny and Robert had to jump through the hoops to get their visas to China, but finally they are ready to travel.
The company is jumping through hoops these days to try to please their customers.
to jump ship: to quit a job unexpectedly
E.g. When the media found about the scandal, several executives jumped ship immediately.
Another marketing agency offered him double his salary to jump ship and start working for them.
to jump in: to become involved in something very quickly, Enter into something enthusiastically
E.g. The fans jumped in to break up the fight between the players.
I will be giving the presentation but since this is a team effort, please feel free to jump in anytime.
to jump down someone's throat: to react angrily to something that someone says or does, reprimand someone
E.g. She's been very irritable recently, jumping down the kids throat every time they open their mouth. Perhaps they should take a family vacation.
Just because I forgot to take out the garbage, you needn't jump down my throat.