1. Have paper, two pens, a calculator, and a draft of the assignment you're working on with you AT ALL TIMES. Whenever you walk around, a person on your team can pull you into his/her office and start talking about the deal. You don't want to be caught off guard. And I say two pens because oftentimes the VP or MD won't have a pen on them and you will look good to be prepared.
2. Add bookmarks for the company sites, 10-K wizard, and to equity research reports. Read these in your down time. As an intern, if you can pull out revenue numbers and tell the story behind a company, this saves time for your team and shows that you know your stuff.
3. How do you develop relationships with senior people? Write down questions throughout the course of the day, and ask them at an appropriate time. The MDs will always be busy and it makes you look like a rookie if you ask questions during team meetings (which wastes time). I often emailed the MDs and asked if they had 30 minutes any time during the week where we could talk about finance, their careers, anything. This worked in my favor when it came to giving out offers, because senior people remembered me. Recruiters told another intern in the group that she did not develop enough relationships with senior people. So keep in mind that not speaking up and not introducing yourself to the team can go against you!
4. If you have some time before your internship starts, and you come from a liberal arts background, it may be helpful to run through some accounting terms on the cash flow statement, income statement, and balance sheet. The MOST IMPORTANT technical skill for an IBD intern is knowing how the three statements of a company are linked together - this is huge for building models and doing any type of valuation. Knowing accounting will give you a huge leg up.
5. At the end of the day, you can't take back a mistake that you made or re-do some work after the deadline. Regardless of the outcome, have a positive attitude towards everyone and everything. At the very least, you have a rich experience under your belt and have learned something valuable for your career and life. And people will like you if you are affable and easy to be around. Knowing finance and doing a good job on your assignments are necessary but not sufficient in getting the offer. Your personality and leadership potential are equally important.