The below are actual lessons I learnt from the mistakes I made in the past 3 months as an investment banking analyst:

1.    Read or listen to the instructions carefully (Listen and note down words for words, or read it words for words. Because otherwise, you might over-do it or under-do the ask.
2.    When your boss asks you to send materials to client/internal party – asking him if it’s the final version yet. If yes, rename the file do not include version number.
3.    Learn how to book a timeslot for printing production instead of printing the book straight away.
4.    When Excel cells are left empty and you are copy value over the table – these cells will be copied over as 0. Make sure to delete, because empty cells is definitely not the same as cells with 0.
5.    ALWAYS save up a version, regardless of how small is the change.
6.    On emails:

• Be on top of all the emails. Literally take every email as an action items. Reply or forward to person in charge. Action on it immediately if the task takes less than 5 minutes.
• NEVER left an email unanswered. If it’s not addressing you – MAKE SURE to follow up with the person who’s supposed to answer it if it’s not answered after a while.
• Read emails every morning when you wake up and every night before you sleep. Check if it’s referred to you (read all the way until the end of the conversation, don’t be lazy, because your name maybe dropped down somewhere).

7.    When cut a cell/columns on excel, make sure to check all the formulas’ reference because it will for sure get messed up (It’s hard to notice because error text may not appear, but all the rows/column especially the sum will get misaligned). Better practise is to clear content/ or delete instead of cutting rows.
8.    If you want to leave early and the rest of people/team are in meeting – send emails to check with everyone if it’s okay to leave.
9.    CHECK and CHECK and CHECK your work again and again. Print it out and read words for words. There is no limit to checking, there is no limit to “being right”. Once things go wrong, it can go really wrong.
10.    Learn people’s working styles
11.    If Excel output is hard coded from email source, add email contents as comments in excel to find sources later.
12.    Read the output – not just copy paste! When executing the task with better understanding of the content – it makes the output 10x better