The poor-boy's approach to righteousness: I've lived rural for a long time, so I can do my shooting in my back yard. While I've built benchrests, I guarantee you that a picnic table is better than a blanket over the hood of a pickup.
There's always the formal rifle range, of course, with benchrests.
Sandbags: I've made dozens. The little zipper-type bank bags. Pieces from the legs of worn-out pants. You don't even have to sew the pants legs. Fold one end over, pour in maybe a pint or so of sand, fold over and hold with rubber bands or baling wire or string. Whatever. Make at least four of them, two of them maybe three inches thick and the others maybe two inches. A couple of pieces of 2x4 can be handy, also.
An old towel under your right elbow saves skin from abrading during recoil.
Target: For all that I have a 100-yard backstop and use regular targets, I also use a cardboard box with a "casual" target that's just a sheet of typing paper with lines that I draw with a Magic Marker and a straight edge. One horizontal line and maybe two or three vertical lines. I use that at 25 and 50 yards for iron sights.
Cost: Danged little. Know-how: Not much, really.
So: You set up the bags so that your sights are very close to being aimed, without you having to hold the rifle. That makes it easy to get a proper sight picture.
Sight picture: My notion is that the top of the front sight should be even with the top of the rear sight. A straight line across is what should be seen. The target should be in the dead center of this happiness, sitting right on top of the horizontal line.
Start at some easy distance, say 25 yards. Adjust the sights for a center hit, being able to shoot a tight group of three or so shots. Then move on out to, say, 50 yards, and repeat. Then go to 100 yards.
With iron sights, I'd guess maybe one inch high at 100 yards for the center of a group of three or so shots is about as good as you'd want.
Now, I don't mean to be "talking down" to anybody. Could be that everybody here knows all this stuff. Like I say, I've just spent a bunch of years poor-boying my way into learning a bit about how to hit a target...
Best luck,
Art