Relax, contemplate your breathing mechanism and how simply perfect it is; slow it down some; then begin counting, from 1 to 10; You visualise the number 1, see its shape, visualise it written as o-n-e as well; Make an effort to do that for about 6 seconds then move on to the number 2, and onwards to 10.. if at any point you get 'internal chatter' go back to the beginning; Think about your breathing, visualise the number 1 etc. if at any point you get 'internal chatter' go back to the beginning; Think about your breathing, visualise the number 1 etc.
This is a useful method for overcoming sleep evasion [insomnia] as well :-)