Do NOT use oil, as that will attract dirt and would get on (and possibly IN) your ammo, which is BAD!

The most important thing to ease feeding is to make sure that the stripper clips are CLEAN.  The brass insert needs to exert some pressure on the rounds or they'll fall out too easily.

The reason most people have trouble loading mags from strippers is that they forget to apply pressure to the REAR of the ammo (just in front of the case head).  If you are pressing too far forward, you'll just stagger the rounds and they won't feed smoothly.

-Troy