Well... there is no single recipe.
Each one of us will walk a different path. We are all different, we possess different attitudes and skills... our opportunities will also differ. In addition, cultural and professional scenarios vary greatly from one country to another. Still, there are some tips that may be valid for many of us.
My suggestion is to come up with reasonably clear ideas about what you would really like to do. You can start from the things you like more than anything else. Start from something that matches your passions and skills, something that feels important and valuable.
Identify the subject you like the most, and then try to gain some hands-on experience. Don’t miss opportunities to participate in practical activities. These may include field work, lab work, data analysis, creative writing or nature photography. You may choose to explore the realms of cetacean management and legislation... or even consider science-based outreach and education. Once you have identified a topic of interest, aim to become an expert in that field, no matter how narrow. Narrow fields will invariably tend to expand, and grow larger and larger over time.
The field courses proposed by various research organisations can be one way of developing basic skills, meet someone experienced, and get valuable advice. These courses may also help finding out how you feel when working on cetaceans from a boat, a cliff, a plane, or a field station. If possible, try different experiences and approach different research groups, before deciding what works best for you. If you "feel good" doing something, then you may have found your own specialty. Go for it!
As a general rule, you have better chances of success if you are driven by enthusiasm and passion.
Take some risks, and don't be afraid of making mistakes... we all make plenty! And we do learn from our mistakes, eventually.
One more thing: do not put your future into somebody else's hands. The key choices must be made by you.
Imagine this situation: you submit an application to be accepted as a student, be recruited as a field assistant, or be hired for a job. You add an elegantly-written, error-free cover letter. You attach an informative curriculum vitae, carefully designed to let your skills come through. Will this be enough? Maybe not.
Your cover letter and CV relevant, but those who read your application may want to know more about you. Therefore, they may google your name and look for additional information, to better understand who you are and make informed decisions. At that point, they may look up your social media profiles, browse the photos you posted, the groups you joined, the people you befriended, or even the music, books and movies you liked.
You would rather not want them to stumble upon... that old image of you looking drunk, or that politically-incorrect statement you happened to make on a bad day, or that link to a gross and stupid video. You say: "But that's my private life! I can do and post whatever I want!" Yes, you can, but by the time that particular information is posted online, it may be spotted by someone who aims to evaluate you professionally. Like it or not, it may end up being appended to your professional profile.
Needless to say, individuals will never be defined by the way they appear on the internet, by the way they look or dress, the colour of their skin, their culture, ethnic group, religion, spiritual inclinations, sexual preferences and so on. These should not matter to your employer or professor. Still, consider that in a selection process, your personal data will be compared with whatever is available about others: your competitors. If your competitors sport a more appealing profile, one of them will be chosen. Not you.
Marine biology is a competitive field... so how can you actually improve the way you look online?
Consider starting a blog or a video channel, or posting your best photos on social media. Let your talents, your style, your creativity become apparent. If possible, show yourself "in action", doing something interesting. Express your ability to engage and commit to what matters to you. In some cases, you may consider posting a selection of your writings, music, artwork... anything.
But be careful: you don't want to be viewed as someone who shows off. Therefore, balance and fine-tune all materials as carefully as you can. You are really sort of "marketing" yourself here. So, focus on the bright side! Smile! Try to imagine being one of those who receive your application amidst a bunch of other applications. Make clear why you should be the first choice. If anyone googles your name, something appealing should come to surface. You want them to say "Wow! This is the person I would love to have in my team!"
Try that, try anything creative... and see if it works.
Choose life by George Monbiot. This one relates to environmental journalism, but is more generally valid.
Clapham P. 2005. Publish or perish. BioScience 55:390-391.
Bearzi G. 2020. Marine biology on a violated planet: from science to conscience. Ethics in Science and Environmental Politics 20:1–13.
Saving the earth as a career: advice on becoming a conservation professional by Malcolm L. Hunter, Jr., David Lindenmayer and Aram Calhoun.
Advice for people interested in a career studying marine mammals by Robin W. Baird
Surviving professional puberty in marine mammalogy: things mom and dad didn’t tell you by John E. Reynolds, III
Advice to students by John E. Reynolds, III
Advice for students by Bernd Würsig
Stanford commencement address by Steve Jobs
The Society for Conservation Biology has assembled resources to assist students in their educational journeys. The web site includes tips on how to make good poster and oral presentations at professional conferences, and on how to write abstracts.
Twelve Tips for Reviewers by Henry L. Roediger, III
This article provides advice to senior scientists, but is potentially useful as it basically discusses work ethics. The article also points out that young and inexperienced reviewers may at times do a better job than the busy seniors.