Do you have your natal chart? If so, choose a time when the moon is applying in trine or sextile to your natal Mercury. If you can have a benefic planet applying in trine or sextile to your Mercury, Sun, or Jupiter, that's even better, and of course doing both is best of all.

If you don't have your natal chart, find a time when Mercury is rising or at the midheaven, and not afflicted by Saturn or Mars.