Stated RTP on paper, luck on the reels
Set your budget before the first spin, since how often the bonus round comes is not known in advance. The result of one session is random whatever the RTP, so one session can end well above or well below what the RTP suggests.
Open the game rules before you play, because which RTP version runs here is shown only there. Two versions exist, and they differ only by a small margin that the rules spell out for each one before you start.
Set your stake with the ceiling in mind, because the maximum win of Starlight Princess 1000 is a ceiling reached very rarely. A win that size is not something to plan around, so plan for ordinary results first.