Normally, I'd simply say "practice and enjoy what you do", but, a few practical hints wouldn't hurt...
1) try to use an, even simplistic, prop, whan possible, or combine foreground environment elements (furniture, items etcetera) and, for full body shots a simply floor panel, with the HDRI dome. Combine that with camera DOF, to focus on the main model(s) of the scene, and generate enough depth, to make the overall render more vivid. How much DOF, depends on your taste, and wether you need the forcus to be dynamic/aggressive or subtle.
2) the make or break detail... eye contact. Luckily, there are a handful of scripts, that do that for you, so the characters have an "alive" eye behavious, instead of that of a doll, blankly staring on... something outside the scene.
3)whenever you are using an HDRI dome for illumination, ALWAYS turn off the camera headlamp. It does add an extra light, yes, but it also flattens any dynamic lighting reactions, that would add a LOT to your render. Combine that with the "1" paragraph. In Iray, and all unbiased render engines, raytracing counts all photon bounces. HDRI domes, acting like a universal light source, don't rebounce incoming light, but objects, without an emmitive value, do. What does that mean? pretty reflections, and color leak over nearby items.
4) finally, try and use a contrasting color scheme between your model and background, when it comes to clothes. In your example case, the pink clothing loses most of its detail value, with all that pink background, but, on a darker one, it would stand out, in a good way.