what does " steering / potency " mean here?
Stone suggests pairing supplements with a food in which they are soluble and "steering" clear of caffeinated beverages.
Finally, Stone warns to take care with storage; high "potency" is best for absorption...
and warmth and humidity are known to deplete the potency of a supplement.

Question

Answer

to steer clear of something means to avoid it.   "Potency' means strength.  a high potency medication has more of the active ingredient in it than a lower potency one.