It is important to think of the context of to whom or what the idiom is
1. on the dot – happens at a particular time, precise time, exactly time.
The class will start at 8:00 a.m. on the dot, so don‘t be late!
2. and then some – and even more; and more than has been mentioned.
It looked like 20,000 people and then some were crowded into the stadium. Investors in
the business got their money back and then some.
3. Find my feet – to become comfortable doing something.
Moving to a new city was difficult as first, but I soon found my feet.
4. read my/your/his mind – W – refers to the idea that thoughts are known by another.
I was surprised he knew what I was planning, like he could read my mind
5. before long – a rather short amount of time.
I will be gone before long, but I hope you learn a lot
6. Cost an arm and a leg – really expensive.
This dress is really nice, but it cost me an arm and a leg.
7. Set in their ways – not wanting to change
My parents are quite traditional and set in their ways
8. (the) bottom line – most important number or information.
My bottom line to do this job is freedom from meddling!
Don‘t give me the details of what the client said about the bid, just tell me his bottom
9. burn the midnight oil – stay up late, esp work late
We‘re gonna have to burn the midnight oil to get this job done by
10. call it a day – end the job (or task) for the day, (or night)
Well, it was nice chatting with you, but it‘s time for me to call it a day