I just do what feels right that day. I can't imagine planning all my exercise for the month.
For a long stretch I was just doing yoga. Then I started hiking on weekends. Then my weekends were full of helping my dad pack and clean so I remembered my bike and have been riding. Then a friend turned me on to zumba so I've been zumbaing, too.
Now that my weekends are mine again, I may hike more, or maybe go visit different yoga studios.
I'll probably bike in the morning, so I'll set out my bike clothes and put a water bottle in the fridge to make it easier.
Try a little variety. It's fun!