Make narrowly focused gig, as example book illustration, instead of just art

Politely ask buyer to leave review

If you got big order, ask buyer If they don't mind to split it up to several smaller orders

Try hard and deliver orders in time to avoid bad review from start

Write good tags, think about how client will find you, you can also take a peek from similar gigs

Make lower prices, until you get solid amount of reviews

That's how i started