The streets of Northbridge — particularly William Street and the surrounding blocks — make up Perth's best and most diverse dining precinct. Chinese restaurants have anchored the area since the 1890s (Perth has a long Chinese-Australian history connected to the gold rush), and the food culture has expanded to cover almost every Asian cuisine: Malaysian laksa and char kway teow, Japanese ramen and izakaya, Korean BBQ, Vietnamese pho and banh mi, Taiwanese bubble tea, and everything in between. Prices are generally reasonable and quality is consistently solid, making this the default answer to "where should I eat tonight?" for Perth residents on a weeknight.
The best approach is to walk William Street from the rail underpass north to Aberdeen Street and see what looks good and has people in it. Quality correlates poorly with appearance in Northbridge — some of the best food comes out of narrow shopfronts with laminated menus. For Chinese, the area around James Street has been reliable for decades. For Malaysian, several good hawker-style spots operate around the William and Francis Street intersection. For Japanese, the ramen and izakaya spots along William Street get busy by 7pm. Book ahead for any specific restaurant on a Friday or Saturday; otherwise, the neighbourhood's density means you will find something good without planning.