The keystone tool of time management is a Planner (other tools are described below). You need this planner to manage your time. This can be a desk-diary, a wall-chart, a teacher's planner, an electronic organiser or a sheet of A4 with dates & times scribbled on it. Whatever works for you is fine, but be flexible: this means stick with your chosen option long enough to know its strengths and weaknesses but switch to another tool if it isn't working for you.
TM4T recommends a specific layout of planners for teachers, and a set of other tools, but the advice below applies whether you use TM4T or not.
1. Keep the number of planners as small as possible. 'One' is probably impossible, but 'two' is reasonable. In TM4T, these are a 'Yearly Plan' and a 'Weekly Planner'. In TM4T, the Yearly Planner is an electronic spreadsheet, which is stored on a memory stick; the Weekly Plan is generated from the Yearly Plan, but is printed out as a single A4 sheet, and carried round in a hard-backed A4 notebook.
2. Keep at least one planner with you at all times. The corollary to this rule is that you need to consider the lowest-common-denominator when it comes to technology and usability. Don't rely on an app if you cannot use it in the classroom; don't depend on a bulky loose-leaf folder if you can't carry it onto the games field.
3. Routines are important and should be pre-printed in your planner. For teachers, a lot of this work is done for you, in your timetable. However, other routines and rituals (eg 'check e-mails', 'lunch', 'detentions, 'gym') should also appear in your daily diary (in TM4T the 'diary' is your Weekly Plan). Avoid having blank sections in your plan when you are actually doing important life-tasks.
4. Your plans should include specific times when you do sort-of-general-unspecified-tasks-in-a-certain-category. For example: e-mails, post, filing, planning. This means that if a task comes up in one of those categories - for example, someone hands you a letter - you don't have to do-it-now, you already have a time allocated for it.
5. Checklists. Task-lists. To-do lists. You should always have a list of things, and carry it with you at all times. This means that you can add things to it, and that you can tackle tasks if the opportunity arises. You should avoid thinking 'what shall I do now?'; instead, just look at your Ticklist (in TM4T, the Ticklist is very precisely defined).
6. Estimation and sequence. When a new task appears (in TM4T these are called 'disruptions') you should add it to your checklist, or to one of your Plans. It's important that you can mentally estimate, prioritize and sequence tasks so they get done at a sensible time, and that you develop your skills of estimation.
7. You need places for stuff. This means the equivalent of an in-tray, and a set of filing locations where stuff ends up. Keep your in-trays as few as possible. In TM4T it is an In-crate instead of an in-tray, which can hold everything from an overdue library book to a lost football sock. Filing needs thought, and TM4T has advice about this.
8. You need to think about what other stuff you need (for example, pens and computers) and make sure they are available in the right place and time for your work-life.