If you're not happy with the course of treatment or the results, say so. They may have good reasons for what they're doing, but make sure that they explain them to you. Fourth, and this is particularly important with serious conditions and recurrances, hope for the best, but plan for the worst. If things do not go well, it's a lot easier if things are settled ahead of time. Fifth, take lots of pictures, especially if you have children.
Film is cheap, and the record they provide of times together are priceless.
Sixth, and most important of all, cherish each day as it comes. Don't worry too much about work, or money, or other things. Enjoy time together, and with your children, if you have any. Time, and friendship, and love, are the most precious things you have together.