In one coures I did, the advice I received for using a pocket mag was as follows:
1) Always put the mag in your pocket the same way. I wear jeans most of the time and the spare goes in my left pocket. Luckily for me the magazine for a Vektor CP1 has a natural lip that catches on the pocket edge, meaning I don't have to fish for the mag, I can grab the base plastic easily. The mag goes in with the rounds pointing away from my midline.
2) Don't put anything else in that pocket (except another mag of course)
3) When drawing the magazine: I get the mag by feel, I don't look down at the mag. While ejecting the empty mag and bringing the new one up to the gun, I work the magazine backward in my left hand so my index finger locates the tip of the first round in the magazine. I simultaneously push back on that round and use that point as an index for insertion into the magazine well.
I agree that proper magazine pouches are better, but if I just need a spare in a jeans pocket, then this works for me.