You'd be amazed how often you think you're printing all over the place and you're afraid everyone can see your gun, and in reality no one notices. I mostly carry a Glock 19 as my EDC. Sometimes I carry with a belly band, a T-shirt, and gym shorts. And I live in a crowded anti-gun urban area. But nobody has ever noticed. Ever. It's just not something most people have on their minds. If you bend over and they see a lump, they'll just assume it's a phone or something. And that's if they even consciously process it. And anyone who might possibly notice a lump and figure out it's a gun is probably also a gun person; someone who is highly unlikely to call you out and cause a stink.
I don't open carry, but I know plenty of people who do, and they say the thing that surprises them the most is how few people notice. Trust me, if you have a gun as small as a J-frame or a PM9 carried IWB at 4 o'clock, nobody is ever going to notice unless somehow your shirt rides up right as they're looking right at your waist line. And even then they might not notice it.
So just carry the gun and ignore it. The more you worry, the more you pull at your shirt or adjust your belt, the more attention you'll draw to yourself. But as long as you have a good carry belt and a good, form-fitting leather or Kydex IWB holster, nobody will ever notice you're carrying.
And that's what I recommend for most people: A form-fitting holster of some kind that will hold the gun securely but still allow a quick and easy draw. And, like BarryLee said, a good, solid belt (combined with a pair of pants that has enough belt loops) can make all the difference in the world.
As for the carry position, I think the best place for most people to carry is in that sweet spot between 3.5 and 4 o'clock (8 and 8.5 o'clock for left-handers). Carrying at 3 o'clock causes to gun to stick out way too much for most people, and at the same time too many people also end up carrying the gun too far back towards the 5 o'clock position. I like the 3.5 - 4 o'clock position because the gun nestles into that spot right behind my hip where it's most concealed, it prints less when I bend over, I can cover it with my arm when walking through crowded places to avoid whacking people with my gun, and it's easier for me to to draw it quickly.
As for the extra mag, you want it on your weak side; the same side as the hand that you use to load your mag. Like JimmyR said: If you ever need to reload or you just had a type-3 malfunction and you need your backup mag, how are you going to quickly grab the backup mag when it's on the opposite side of your reloading hand?