Okay, here is a plan to get better:
1. Get yourself a Nikon 35mm f/1.8 or 50mm f/1.8 (or, if you're poor, the Yongnuo 35/2 or 50/1.8 for Nikon mount). Read up on what aperture is, how to set it on your camera, how it affects your exposure, how it affects your depth of field, what depth of field is, etc.
2. Get yourself an off-camera flash. The Lightpix Q20II is pretty good and relatively cheap. If that's still too much for you, find yourself a manually-controllable flash with a tilt-swivel head and you can use it on-camera but bounce it off a wall or something.
3. Go to the Strobist blog, https://strobist.blogspot.com/
, and read their Lighting 101 series to learn how to use that flash you just bought.
Learning to use indirect flash will VASTLY improve your photography, and switching to a faster lens than the kit will let you get some narrower depth of field that'll give your photos (for better or for worse; a lot of people consider this a gimmick) a more professional look than you get with your 18-55.
4. More longer-term, find some really high quality porn. E.g., look through Reddit's 'nsfwfashion' subreddit or similar. Look at how those photographers frame and compose their shots and pose their models. Try to emulate those styles; figure out what works, then branch off from there to develop your own style.
5. Take a shitload of pictures. Every minute spent practicing makes you get a little bit better.