Walking across the stage
It may seem obvious but an internship is absolutely critical. As many internships as you can fit in before you graduate or even after if you can afford it, the better. Keep in touch with people you work with - almost all the jobs I've ever gotten have been through someone I've already worked with mentioning my name. This is particularly hard for me as I am actually kind of shy and calling a boss or collegue out of nowhere to catch up is really hard for me. This is probably my personal biggest handicap - my advice for others is to get good at this.
Be confident in your abilities. No one knows everything but each person brings their own set of skills to the table and it is important to know what your skills are and be able to convey that to your employers. Take every opportunity to learn something new in your field and be flexible. Most people want to be in a certain niche - editor, producer, director, grip, camera, etc. but when you are starting out be willing to do ANYTHING. You will not just fall into exactly what you want to do and be able to make a living off of it right away.
Be prepared to be unemployed. I mean that both financially and emotionally. The nature of the industry is that you are hired on a project to project basis. That means when one project ends you are on your own to find the next one. The better your networking skills and the higher people think of you the easier it will be to find your next project but inevitably at the beginning there will be gaps. This is what ends up driving a lot of people into other industries. Being broke and unemployed is no fun. It starts wearing on your confidence if you let it. I strongly believe the longer you stick with this career the bigger a network you will eventually have and those employment gaps will get shorter but even professionals who have been in the industry for many years still have gaps.
Be professional and don't burn any bridges. You may not like all your collegues and you might think some jobs are too low paying/low skilled but you never know where your next recommendation is going to come from. Be nice and professional with everyone.
Lastly, my favorite job hunting sites are Mandy.com and Craigslist.org. This is because they are free. I am going to try to expand my job hunting horizons a bit and try some new sites that have been recommended (media bistro being a recent one) but they are my go-to sites. I have gotten a couple jobs off of them, which is actually pretty good since almost all jobs in this industry are word of mouth.
Hopefully this helps some recent/soon to be grads in entertainment. If anyone further along has advice for me please let me know. I am still learning and getting my feet under me as well.