There's no knack; it's quite straightforward.
If your chain seems right when you adjust it, but seems wrong later, it's probably because your chain's a bit worn and has some tight spots.
There's no need to use a paddock stand, in fact it's not a good idea, cos you're not comparing like with like when you measure the slack; just put the bike on the sidestand.
And generally people tend to adjust chains too tight: err on the slack side.