First of all, ASO is most key element for any app on the store. ASO defines the existence of your app.
Keywords start with ASO, have a look at your own app, and define it with words. Is it a VPN or QR Code Reader app, maybe a Endless Running game. You should start by writing down a full description of the app, which could be used on the app store.
After you've done this, you should find the perfect name, this i very hard, as it should be short and clean, but still have keywords in it. But e.g. a VPN app shouldn't just have a title called "VPN", it should be something with a brand like "Go Anonymous - Free VPN Proxy". This way you're both showing of your brand, but also going to rank on the most searched keywords for VPN apps (VPN, VPN Free, VPN Proxy).
Keyword field
The App Store has a special keyword field, where you can put in up to 100 characters, which isn't much, so it's really important to think about the most relevant keywords for your app, and don't duplicate any words.
Subtitle
A very short description that is intended to summarize your app in a concise phrase.
App Previews
You're able to upload short videos/previews of your app, these can be up to 30 seconds long. If you have the opportunity to make a good one, then you should always include one, as it will help you overall ASO.
Screenshots
While it can be hard, to always include everything from your app, within only 10 screenshots. You should definitely do your best, and try to capture some key screens/moments in your app, which is showcasing the purpose.
Promotional Text
This area could be used, to share your latest deals or news, as you can update it at all times. It appears at the top of the description
Then you're always able to contact us, it can be done through our Live Chat, Skype or by Email, that's up to you. All of these methods are found at the bottom of each page.