I'm sure I need to improve my body posture, but it hasn't been my focus. Do you have any suggestions for where to start with this?
It's difficult to give clear steps that are applicable for everyone because the exact way your body is unbalanced depends on the weakest links in your postural chain and how the rest of the musculature is compensating for them.
However, typical problem areas where muscles are not activating in a balanced manner are: neck and shoulder area, hip & groin area and the pronation of feet. Your feet, hips, shoulders and head should be aligned in one straight line. If you're spent years sloughing, a lot of forceful stretching needs to be done daily. I stand in front of the mirror and try to "see and feel" my way into a better posture by making corrections based on how my reflection looks and how my body feels.
Breath is also a good guide. If you try to take deep breath into your lungs and simultaneously kind of fight against the breathing with every muscle in your torso, including the back (basically all the musculature around the lungs), you start to get a feel for the various core muscles that are supposed to be supporting the body all the time.
All in all it's a very intuitively done way and if you're low in such intuition I'm afraid this is not very helpful. For me it was easiest to just get my hands dirty by flexing and stretching muscles and figuring out how mechanics of the musculature are intended to work. Smoking a bit of sativa helped in creating a better mind-muscle connection too.
It takes perhaps 1-2 months of almost daily work to reach an anatomically optimal posture and train your nervous system to remember that.
I don't remember if I've posted this already but here is how I used to stand before improving posture vs how I stood a couple of weeks in. Notice how much forward the hip area has come (as a result stomach and butt don't stick out so much).
Good posture also improves blood flow to the testes, which can make you feel and act more manly.