1. Clear mind-1. Write down and 'forget' the stuff you don't want to consider at the moment. Put it aside for later.
2. Clear mind-2. Walk to gain perspective and oxygen. Sip water.
3. Clear desk. Have at least your main working area free of too many physical distractions.
4. Clear process. Request/insist on some interrupt-free time. From people, from mail, from phone.
5. Clear issue. On what do you want to focus? Define it.
6. Clear action. Get to work.