The ability to analyze accounting numbers critically is important in most analyst positions. Ultimately, you should aim for the CFA designation if you would like to be a securities analyst. The CFA helps you become much more mobile over time. If you have ambitions too "bail out" some day and become a corporate financial analyst you might also want to consider the CMA (Certified Management Accountant) designation.
It's hard to define what makes a good trader. A good understanding of the market, quick reactions, analytical skills and the ability to bluff help. Read Liars Poker by Michael Lewis to learn more about sales and trading.
Most large firms operate out of New York. Even if you are interested in working in another location, your general interviewing activities are likely to be centered there. Other places you should look at include Hong Kong, Tokyo, London, Moscow and Singapore. If you go looking for a job in investment banking using informational interviews it is crucial that you make several trips to New York.
The key to breaking into investment banking is a good network of contacts. You may already be blessed with such a network, but if you don't have one, you can start to develop one by going on informational interviews, attending industry conferences, finding alumni from your school in the business etc. Keep in mind that your network might not really "pay off" for some time. If you are young and haven't gone for an MBA degree, try to get into the best possible school and then go for quantitative and analytical coursework.
Starting off in an investment bank, you are usually responsible for getting projects done well and on-time, whether it be writing reports, running spreadsheets, trading, doing research or coding programs. Later, once you get involved with clients and ideas for generating revenue, you will be rewarded greatly if you can bring in business. At higher levels (usually Director, Managing Director and up) you are exposed to much greater risk. At this level, people are often fired for non-performance, whereas at lower levels you may not be scrutinized as closely.