Go from the last beat of the measure to the first beat. You would not use vibrato on a weak beat because it draws undue attention to it. Use vibrato to help show the strong beats. Your audience does not have the benefit of seeing the music so you have to show them by how you play what is on the page. The more clearly you speak the language, the more effective your performance.
Vibrato is unnecessary in rapid passages.
It sounds fussy and affected. Above all, remember to use vibrato to enhance the phrase. Vibrato is not a switch on an electric organ to turn on and use indiscriminately. Above all, have fun as you learn to incorporate vibrato into your playing. Vibrato adds color, vitality, and interest, both for you and for your audience.