Keeping a fitness journal is a good idea.
Not only does it help you keep track of your activities, it helps hold you accountable to your plans. You won't remember the activities you do after a week or more, so record your fitness endeavors. Not only can it help you determine what you're doing right, but perhaps what you might be doing wrong as well.
Check out Jeff Galloway's blog about why you should keep a journal. It doesn't have to be overly complicated. I use a simple notebook with entries for every day.