Trader

1) Go to the company website and see the job posting.
2) Apply and pass their pre-screening.
3) Get a phone interview. Prepare by googling trading and market making interviews. With enough research, you should have a good idea about what they will ask you. It's going to be the usual "why trading", "make me a market on X", "what is put call parity", etc. Portray yourself as analytical, team-oriented, ambitious, and slightly aggressive.
4) Do well in the tests they give you. Either be smart, or practice as much as you can if you're not. There are a variety of tests you must take, ranging from behavioral to speed-based.
5) Get another phone interview. Follow same strategy as 3. This time you'll most likely be interviewed by a head trader.
6) Get an invitation to the superday. You'll do math tests, a group presentation, and multiple panel interviews. The questions won't be too hard, but you need to make your case logically and confidently. If you can do that, nail the tests, and be sufficiently personable, you should get the offer.