Reviews influence both where you rank and whether people choose you. A business with 80 reviews at 4.8 stars will usually beat one with 10 reviews at 5 stars.
Ask at the right moment
The best time to ask is straight after a job is finished and the customer is happy. Send a short text with a direct link to your review form.
Reply to every review
Replies show future customers that you care. Thank happy customers by name, and answer unhappy ones calmly with an offer to put things right.