So, here is what *I found* was most helpful to me from 1976 to 2000 in my film SLR era, and the many customers I sold cameras to years ago, at the beginning of the 35mm autofocusing film SLR craze. A medium telephoto lens with an f/2.8 maximum f/stop: the 135/2.8 in the 1970's and 80's: on a DX NIkon the modern mostly-equivalent lens would be the Nikkor 85mm f/1.8 AF-S G, at just under $400 brand new. A reallllllllllllllllly good "first telephoto". Easy to afford, easy to carry, easy to envision the look of, and very sharp and crisp, and at 127mm e-View on DX Nikon, a really useful, moderately narrow-angle lens.
A 28mm f/2.8 moderately wide-angle lens; on DX the modern mostly-equivalent would be a 20mm prime lens, and the new Nikon 20mm G-series would be a good one. On a budget, the Sigma 30mm f/1.4 lens would be a VERY nice lens...it has nice bokeh, and good speed of f/1.4 and it is designed for DX...I have seen used ones as low as $125 here locally. The new plastic fantastic Nikon G-series f/1.8 lenses are very good for the money. The 50mm and 85mm are the lowest cost models, and the others are more expensive.
A 90 to 105mm macro lens, or a 180mm macro lens. This is a great tool. Tamron 90mm AF-SP would be my suggestion, make sure it is a newish one that has the in-lens focusing motor, so your current camera can focus it. The longer, the better, in my book. Skip the 60mm macro, and go for a 90 or 100 or 105mm on DX.
A 12mm or a short extension tube. Kenko AF tube...you WANT an externsion tube that has AF contacts in it for use with that camera. The 12mm tube is the handiest.
A GOOD speedlight and a Nikon SC-28 or SC-29 flash connecting cord. The Nikon SB 800 is my favorite. A speedlight and a 1-meter pigtail connecting cord is super-handy.
You can do a HUGE amount with a semi-wide-angle lens, a medium telephoto of fast aperture like the 85mm f/1.8, and an extension tube for close-ups with it, and then a speedlight used on an SC-28 or SC-29 TTL remote cord, for both close-ups, for bounce flash portraits, and for flash in left-hand-on-cord-and camera-in-right-hand flash work where you can lift up and angle down the flash, so its beam creates a bit of directionality to the bare flash light, and throws the shadows down and to the right of people.
The idea is this: get THREE good, fast prime lenses that are easy to learn to see with, and which are not of limited use, and which do not make BORING images. The MOST-boring crap comes out of ultra-wide and wide-angle lenses used by intermediate or new shooters, trust me (10-20,10-22,10-24,11-16,12-24mm lenses....ugggh,please, no)...it takes a LOT of discipline, and training, to use lenses with wider than 90 degree diagonal angular view. The drop-off in size of things beyond 5 meters with the wide-angle lenses make for HUGELY boring images in many situations. Your 18-55 is an okay normal lens.
Try learning to SEE and compose with a semi-wide, a normal, and a medium telephoto, as well as to see close-in, small scenes, using the 50 or 85mm lenses and a 12mm or 13mm extension tube, and very often, a speedlight flash on an SC-28 cord.
TO recap: A medium telephoto lens; moderately wide-angle lens;macro lens;short extension tube;GOOD speedlight and flash connecting cord. That is six things.
A 35mm lens is the normal, and a 50mm/1.8 AF-S G would be a short telephoto. I find "normal" to be boring, and prefer the semi-wide or the short tele or medium tele options.
Leave the macro lens for last if you want to, and pair the extension tube with the 85mm lens as a substitute.