There is, of course, a lot more to it than that. Yet, even with all of our 21st century medical knowledge behind us, there's still only so much we can do. And if you think that cancer is a "battle" that you can win, please see the following: http://zenofmetastasis.blogspot.com/2013/03/honk-if-youre-hero-ps-you-are.html
But there are a few practical things you can do after a cancer diagnosis that will give you the best chances right from the start, and I'd like to go over them here.
1.) Seek out the best doctors you can find that specialize in your type of cancer. This probably ties as one of the most important things you can do. Do it quickly; don't waste time. The minute I got my diagnosis, I was on the phone scheduling appointments. However, I wasn't in my right mind, and I didn't even think about finding the best possible doctors available to me. When my mother got wind of things, she immediately researched the melanoma gurus on the East coast and called to get me appointments. I had to cancel all the plans I'd made, much to the chagrin of the administrative assistant who'd helped me schedule them. So, do yourself a favor, find the best doctors right away, or run the risk of having your mother do it for you.
2.) Find your support network. This is the other step that ties for most important. You cannot suffer through the terrors of cancer without a support network. Period.
3.) Do your homework. Don't blindly follow along with any treatment plan you're given without reading into it extensively. I had a bit of insurance trouble throughout, but living a middle class American life, I was entering into a veritable wonderland of technological and medicinal options to treat my cancer. However, many of these options are touted by the people who fund them, and they may represent particular agendas that don't include your best interests as a patient. Be aware that we live in a complex and morally ambiguous world. Do your own research and be your own advocate.
4.) Make lifestyle changes if necessary. I had been smoking when I got my diagnosis (a few cigs a day) and I'd been working a highly stressful job in the deep and terrible trenches of corporate NYC. Most nights you'd find me partying my heart out, drinking away the stresses accrued during the day. If you asked me now though, I'd tell you that it's easy to see how a "work hard, play hard" lifestyle falls directly into the realm of things with adverse health affects. I'm not saying you shouldn't have fun. In fact, I'm a big believer in the importance of fun and adventure, just be careful that you aren't seeking out your fun as a means to distract from all the bad parts of your life. Of course, lifestyle alone is not going to kill you, for the most part. There are certainly behaviors that are more dangerous than others, like smoking, or chowing down on discarded, depleted uranium cores. However, there are those miraculous individuals who do everything wrong and still live to be a hundred. These people are few and far between though, and no one knows what makes them so resilient (if they insist that they do, they're trying to sell you something). In reality, until we know exactly what we should and shouldn't do on a genetic level, it's a good idea to lower your own risk factors as best you can. It's very possible that the primary cause of most cancers is a genetic disposition (this is certainly true in certain cancers, if not all of them), combined with an individual's risk profile. A genetic disposition doesn't guarantee that you'll get cancer, or that cancer will return. But a genetic disposition aggravated by a life full of excessive risk factors just might.
Read more about stress and the immune system, here: http://www.cancer.gov/cancertopics/factsheet/Risk/stress
There are other, optional things to keep in mind also. These are things you can do in addition to the list above, and may or may not jive with your current goals.
5.) Move home. Be wherever your family is. These people are important to you, or they should be. Maybe you're estranged from them. Well, fix it. Having been diagnosed with cancer, you now realize that life is much too short. I was fortunate enough to have a very supportive family throughout my life who were there for me during my surgeries and treatment. I tried very hard to stay in NYC and go through this without them, but I quickly realized that I couldn't, nor did I have any right to deny them precious time with me in case I might be dying.
6.) Find your friends. My friends are everywhere. I hated leaving the ones in NYC. They had become a second family to me. When I moved home to Pennsylvania though, I quickly fell back in with the close-knit group I'd grown up with. And I had new people connect with me to show their support, too. Some I'd never talked to before, and some I hoped to talk to much more. One of the best things about cancer is that you'll quickly find out who in your life really belongs there. Some people will disappear. And others will be more supportive than you could have imagined. These people, the ones who stick with you, are the ones you need to survive, and not just through cancer. Carve their initials deeply into your heart, and make sure they know how much they mean to you.
7.) Find your religion. I don't care what it is, and I'm not going to tell you about mine. Most people wouldn't appreciate it if I did. And that's fine, because it's for me, like spiritual beliefs should be. They're personal beliefs unique to each individual, and we use them to find our place in the universe. And don't push your individual religion on someone else once you've found it; that doesn't make you "pious." But do use your beliefs in whatever way you need to help you overcome your fears and live a more fulfilled life in the face of your diagnosis.
8.) Quit your job and do what you love. This one's simple. There are many who don't have this option available to them, but sometimes it's easier to focus on dealing with the side effects of treatment rather than on your career. If you can afford to, do it. And, if you hate your job, do it with a smile on your face. Afterward, go after that thing you've really wanted all your life, and make no excuses until you get it.
9.) Reevaluate your priorities. That is, if you haven't already done so. I did so immediately, within nanoseconds of being told I had cancer. I cataloged my greatest sins, and set out to atone for them. Usually, our greatest sins are straightforward and easy to identify. Mine was. And if you have the energy, don't just identify your failings, set out to fix them. Then, seek out the most important people in your life and tell them about it. Spend as much time with them as you can. Find the other things in life you know to make you happy, and don't ever lose sight of them.
I set out to write a guide about surviving cancer, but I realize that a lot of these things aren't cancer-specific, and you should probably be doing them anyway, regardless of what diseases you have or don't have. Or, if you hate all of my suggestions, that's okay too. Because this was my guide, and it consists of all the things that were important to me throughout my experience with cancer, and still are. But please, if you take nothing else from this, use it as inspiration to find your own guide. Because there are important things in your life that you can't live without -- I know there are. And if you haven't figured out what they are yet, take it from me -- If you wait until you might be dying to find them, you'll end up having a lot of apologizing to do, and mostly to yourself.