There are 2 main things that I'd wish I had known much earlier.

1. Don't try to be something you're not. Use your own experiences

Having cancer changes you and if you are constantly trying to do something that everyone else does you are putting yourself through unnecessary hassle. For example I studied business in university and went into the corporate world with the idea of wearing a suite to work and becoming one of those over paid business men because most of my friends were and I had the impression that thats what the end goal in a career should be. After 4 years of struggling everyday to measure up to all the high-fliers in the business world. I decided to switch careers to teaching and use the experiences I have to help others going through a tough time. It was the best decision I have made. I don't struggle at work and do what comes naturally to me, I enjoy what I do and am not overly tired at the end of the day.

2. Learn your limitations, but don't let them define you. life after cancer is harder, not impossible.

There are a-lot of things which become harder after treatment i.e. balance, learning knew skills, organisation etc . . . However that does not mean that you should believe that there is no point on working on them. Most of these can be improved as long as you realise that it will take more effort then others and sometimes different approaches need to be adopted.
When I was in Uni, I shied away from a lot of new things because I thought that there was no way to achieve them. 1 example being Martial arts and sports. I have worked hard and consistently on these areas and am now a senior grade belt in Kickboxing which I never believed possible after my operations. On an organisation front, I always use to forget things and couldn't cope with keeping an up to date inventory for my medicine and to do list ect . . .I now have made a visual timetable for my self with removable velcro pictures of my medicine or other things I usually forget and this has helped me to stay on track with what I need to do.
I guess in conclusion I am trying to show that despite limitations success is possible with the right guidance and mindset.