New to the concealed carry world(still waiting on my license to come in)… and have been doing a TON of reading. But it seems more information is just adding more decisions to make.
Such as type of Holster, IWB, but what position, cant, ammo…Was wondering if anyone could just give some pointers in where to look, what you do, why you do it? Needing a good starting point!
Have you already made some decisions yet, like what firearm you want to carry? If you can give us an idea of what your constraints are (office “non-permissive environment”, suit & tie vs casual clothing, etc) we can maybe be more specific in helping steer you in the right direction. I’ll post some about my experience below in case it helps.
There is some good advice already here in this thread especially from @Craig6 and @Fred_G . Ultimately though, there is a lot of trial and error as every person’s body shape and nooks & crannies is different. I too have a box full of old holsters.
If you plan on carrying on the waist, a good gun belt is super important. In fact, maybe the most important. A stiff belt helps prevent the firearm (and maybe spare mags, etc) from sagging your pants down, and keeps the firearm in the position/cant you placed it. Characteristics of a good belt is that is is stiff, durable, and adjustable in small increments.
I have a good opinion of Kore gun-belts (their leather ones fit right into an office environment), and I use Volund Gearworks “G-hook” belts daily. They have a normal weight one and a “slim” weight that is more flexible which I use when I have a lighter firearm and/or and moving around a lot (like yardwork). There are many reputable gun-belts around, those are just the ones I have experience with.
I personally carry appendix (link to EDC in another thread) as I found that to be the most comfortable and easy to conceal for me. I’m short (5’6" 170, built like a former athlete 
so not super fit, but not chunky either). I’m a web developer, so I wear t-shirt and jeans/shorts/cargo pants every day (basically really casual, but not sloppy).
Carrying at 3 o’clock made my waist look really wide so I just looked like a square shape. No one could tell i had a firearm, but they could see i had something on my hip. Anyone remotely paying attention would assume it was a firearm.
Carrying at 4-5 o’clock-ish was actually really comfortable, and concealed very well when i was standing or walking around, but whenever i sat (remember I’m in t-shirts) it printed like a mofo, and every time I stood up i’d have to adjust my t-shirt over the gun since it had a tendency to slip in between the firearm and my body just a bit.
Carrying appendix works best for me in terms of concealment and comfort. Concealment, literally no one knows I carry except for the few people who know where it is and even then they can’t see it. Sitting down, standing up, twisting, etc it all stays put. It is a little counter-intuitive, but a longer slide length is helpful here as it prevents “tip-out” where the butt of the firearm leans outward. Think of your belt as a fulcrum point and you need at least a certain amount of firearm above the beltline in order to get a good grip, the remainder is below the beltline. If you have more above the line than below you are likely to get that “tip-out”. Even though I usually carry a Glock 26, it is in a Glock 19 holster. My Glock 43 holster is “long” to get a similar effect. Both holsters are from JM Custom Kydex. For AIWB having a “claw” of some sort helps tilt the firearm grip back towards your body. About 80% of the time I carry the G26, but sometimes just a certain pants/shirt/“i ate too much” combo makes it not conceal great so on those days I carry a G43 instead.
For comfort, it took some work to find just the right spot where it doesn’t hit a pelvic bone when sitting, and also adding a neoprene wedge was super helpful. You might carry right at 12 o’clock or maybe a little off to the side 1 o’clock or even further at 2-2:30 o’clock to find that safe spot. You may have to adjust when sitting down/standing up, but I usually don’t have the need to if I put it in the right spot to begin with.
I have a good friend who carries a Sig P250 in a belly band. He finds it super easy to conceal and is very comfortable for him.
If you have more specific questions, would be super happy to help answer and I’m sure others on here who carry on their hip (or shoulder, ankle, pocket, off-body)