I have been to the mountain and heard the words of the gurus. I am referring to @RandyHayes , @WarrenBelz , @Shanescows, @mdevaney and others too numerous to mention. I now return with some wisdom for my fellow PowerApps sufferers who have been lost for 40 years in the SharePoint desert. Here are my Ten Commandments (feel free to disagree)
The 10 commandments of SharePoint in PowerApps
Thou shalt use only Single line of text, Numbers and Date/Time type columns.
Thou shalt use a separate list instead of the Lookup column type and connect the lists between parent and child tables with the parentID as a number column in the child table.
Thou shalt strive to use delegatable functions and operators in all formulas
Thou shalt not use spaces or special characters in column names
Thou shalt not use these reserved words for naming columns:
Thou shalt not change column names once they are created or repurpose the holy Title field.
Thou shalt use IntelliSense to find valid options and values in formulas.
Thou shalt reset required fields to not required in SharePoint and use PowerApps to make them required. If you cannot reset a required SharePoint field, give it a default value (this applies to the Title field in particular).
Before building your PowerApp from scratch, go to your list in SharePoint and select the PowerApps dropdown and let PowerApps build your app for you. It's a good starting point to build from.
Thou shalt consider using a premium connector like SQL or Dataverse if your list will exceed 4000 items.