The name is the strongest field you have
Apple weights words in the app name above words anywhere else. That makes the 30 characters the most valuable space in your listing, and it is why a name that is nothing but a brand gives away your biggest advantage.
The usual shape is your brand, a separator, and the job the app does: "Pocket Chef: One-Pot Meals". The brand still leads, so the page reads like a product rather than a keyword list, and the words after it are the ones people type.
A name that is only a brand wins only searches for that brand.
The subtitle is a second line, not a tagline
The subtitle carries real search weight, second only to the name. Spending it on something atmospheric like "Simply better" throws away the second most valuable field on the page.
Use it for the terms that did not fit in the name, written as a phrase a person would say. It sits directly under the name in search results and on the product page, so it is read by humans as well as indexed.
Do not repeat a word between them
Apple indexes the name, the subtitle and the keyword field together. A word in the name is already counted, so repeating it in the subtitle buys nothing and spends characters you cannot get back.
Check the three fields as one set. Every word should appear exactly once across all of them.
One word, one place. Repetition across the three fields is pure waste.
Watch what gets cut off
Search results truncate long names on narrow screens, so the most important words should come early. Write the name so that the first twenty characters still make sense on their own, because on some screens that is all anybody sees.
ASO Studio