About recommendation letter

Hi,

I asked my ex-company's boss to help me to write recommendation letter and he promised to write it for me. However, I am still preparing for TOEFL exam now but he will leave the company soon. What can I do now?

1) Ask him to write the letter now

or

2) Wait until I begin to apply.(At that time, he should work at a new company)

Any suggestion will be appreciated!

is there any examples or hint on reference letter writing? My recommender asked me to provide some example.