You too can write Kushiel's Dart (and it's variations)! Here's a short guide: 
 The World / D'Angelines: 
 D'Angelines are beautiful. They have beautiful people, beautiful food, beautiful wine, their language is beautiful, their lovemaking is beatiful, and everybody farts flowers. All the other non D'Angeline savages are not beautiful, so they are not worthy of D'Angelines. Ugly but noble and brave is acceptable, even though, *grits teeth* they might dilute the perfect D'Angeline gene pool. They even have a song for when they're stuck in ugly-people land far away from home. 
 World Building: 
 Instead of building new worlds, why not use hackneyed stereotypes of the real world and change the names a little bit? 
 D'Angelines = French (beautiful people, wine, women and song, etc) 
 Cruithne = Scots (noble savages) 
 Skaldi = Germanic tribes (just savages) 
 Tsingano = Gypsy / Roma (fortune tellers, travellers) 
 etc 
 The Language and Prose: 
 Use as much purple, fruity prose as possible. Describe everything in superlatives, and be sure to use the most lofty words for everything. For example, replace all occurences of 'brown' with 'bistre', all occurences of 'black; with 'sable' or 'raven'. Use fruity terms for sexual acts too - instead of oral sex, keep calling it 'languissement'. 
 When a beloved person dies, say things like 'Ah, no. No', it imparts more gravity. 
 Don't forget to FORESHADOW EVERYTHING. 
 The main character: 
 She has to be perfect, with absolutely no character flaws - beautiful, multi-lingual, kind-hearted and loved by everyone. Even her 'flaws' are loveable. 
 Make sure she's horny all the time, even when she doesn't want to be. They do that all the time in Hentai! Being ravished by tentacle monsters whipped and tortured with various implements is always a pleasurable experience! 
 The solution to everything: 
 Sex. Sex solves *everything*.