It's not too hard if you have a proper PCB with solder resist. The surface tension of the solder causes it too glob onto your part's pins and the pads below them. The solder resist is really key here, or else it's essentially impossible.
You will have to test for solder bridges between pins, and maybe use some solder wick to get any excess out.
It's not super fast, but it's absolutely doable with an hour or two of practice. Solder paste and a heat gun is the next step up, which I find more difficult to get right (I'm bad at applying the paste).
If you're using solder paste the trick is to get a stencil along with your PCB. It has holes where solder should be applied which you place over the PCB, smear the whole lot with solder paste, and then drop the components into place. You've now got solder exactly where you need it and nowhere else.
I find stencils hard to use ... I always end up smearing them when removing the stencil.
Mind you, I have pretty minimal experience, so maybe I just need to try more and get the hang of it. Unfortunately without owning a hot air gun or reflow oven, I'll just keep avoiding bga parts and doing everything else with an iron.
