To begin with, a rant:
There are an overwhelming number of topics on this site from students / graduates about which firms to apply to depending on their personal field of interest. While some, I think, are excusable (and can be chalked down to naivety or a lack of experience), the vast majority strike me as unreasonably lazy / clueless. After all, why on earth should Glencore hire you as a junior trader if you can't even demonstrate the nous and initiative to f*cking Google "top commodity trading firms for graduates"? There's a wealth of information on a number of different websites specifically for people in your situation, and yet you expect a job without doing any of the initial legwork yourself? It's inexcusable. I certainly wasn't this gormless as a uni student, so there's no reason why you should be.
Right, now on to the advice:
Firstly, how to determine which firms to apply to. Google is your best friend here. Simply search for: i) The industry; ii) Your desired role; and iii) Your geography. This will generate a huge quantity of employers for you to examine and, gradually, refine into a comprehensive list of firms you actively want to work for. There are also a number of league tables published for various different employment sectors (both formal in structure, and informal). Look these up and use them to help inform your application choices. Economics undergrad at Harvard with a 4.00 GPA? The world is your oyster and you should generally work from the better firms (in your list) to the worst (after boshing out a few practice applications to sharpen your profile). Anthropology undergrad from a state university with a mediocre GPA? Still well worthwhile applying, however quantity will ultimately prove your ally. Crucially, regardless of your standing, create a list of firms from top choice / most likely destination to least preferable / long shots.
Secondly, add structure to your approach. When I was going through the reps of applying, I made a master spreadsheet on Excel (you're going to be using a lot of Excel over the coming years, so might as well become chummy now). Mine was structured similarly to a Gantt chart. Going down the y-axis were the names of the companies I'd applied to, the role, the region, and a link to the application portal I'd applied through (incl. a record of my username and password). Along the x-axis were the different stages of progression I'd fill-in as I progressed: application >> online assessments >> phone interview >> first stage interview >> final stage interview >> offer. This let me quickly and clearly identify which applications I was still working, and how far I'd progressed to date. Enter interview dates into the relevant cell to help you keep track of those too.
Thirdly, prep hard for interview. Again, structure is your friend here. In a similar vein to the aforementioned spreadsheet, I used to make a master Word document that I actually used to take to interview as a comfort blanket. I can't remember ever actually referring to it in interview, but I always knew it was there if I truly got stuck, and it gave me something to read and review in between meeting whoever it was that happened to be grilling me that day. The structure of the document was as follows: i) Interview details - the date, time, location, who my contact point was, and any other relevant notes; ii) About the firm - description of the business and its different business lines, key financial highlights; iii) About the job / programme itself - rotations, my preferences, reasoning; iv) Technical notes - valuations, recent market prices, a brief crib sheet for quick referral should I draw a blank; v) Application details - any questionnaires I answered and what my response was; vi) Recent news - both about the market of interest and the firm itself. Some of these documents went in excess of 8,000 words. Goes without saying that I also brought a copy of my CV and cover letter, just to make sure I had them in front of me for reference.
Finally, presentation. I've recently got to the stage in my career where I've been asked to interview. Here are some personal pet-peeves that, I hope, will help steer you in a better direction:
1) Don't over prepare - I hate candidates that seem too rehearsed. This isn't to say you can't be polished, but if, after every question, you recite a pre-prepared statement, I will bin you. It shows a reluctance to engage and adapt, and - frankly - it comes across as weak.
2) Speak clearly and confidently, and freely admit when you don't know something. Don't amplify your achievements: state them as-is. If you try and bull sh*t me, I will ping you on the spot.
3) Be willing to have fun. Although HR gives me a recommended list of question to ask applicants based on their level of expertise (e.g. spring week, summer intern, graduate analyst), I tend to go off-track and instead get to know the person themselves. If you reciprocate, and it seems to me like you're enjoying yourself, I'm far more likely to want to sit next to you for the majority of my week.