A work diary or daily planner is something useful for time management for any writer. It is possible to buy a cheap one, however I'm going to talk about one in particular that seems to have everything a writer needs.
It's the Daily Planner from The Organised Housewife:
here
Some of the ways in which this planner is useful are:
Goal setting
Every writer needs to set goals. Maybe this doesn't seem necessary when first starting out but goal setting is a necessary part of the writing business. This particular planner lets you write down the goals for each month and it has a checklist so you can tick off each goal. This is useful for if you want to complete a certain amount of words in a month or edit a certain amount of chapters in a month.
Keep track of appointments
For each month of this daily planner there is a month at a glance. This is useful for keeping track of appointments that might be necessary for a writer. For instance you could schedule your book launch party, a book signing, a visit to the accountant and other appointments.
To-do list and schedule
Busy writers have a daily to-do list. For instance you might want to write down how many words you are going to write that day, update your facebook page, update twitter or write a blog entry. There is also a schedule on the left for when you are going to do these things. This planner has a to-do list and schedule for every day of the year.
Meal planning and water tracking
Knowing what and when you are going to eat can be useful when writing. This planner has a page each month for planning dinners as well as a section each day for planning meals. You can also track how much you've had to drink each day.