Are you asking for any specific interaction, aspect, or in any particular period? the nawha who first encountered the spaniards had a different perception of them than those that dealt with them 100 years after the conquest so I cant think of any particular generalities on this point.

As a precaution I'll just post the first report Moctezuma II could've received of them, from Alvarado Tezozomoc's Chronicle of Mexico, Chapter CVI (translation by me):

...lord, unknowns have arrived from the edge of the great sea, they were fishing with rods and nets until afternoon and then using a very small boat they would then enter 2 big towers (we assume this is describing their ships rather than Cortez's temporary settlement) and climbed unto them, they were about 15, with colorful clothing, blue, green, and a color like dirt that looked like our ychtilmatle (a type of clothing), but very ugly, and also with a color that was skin-like, others with colored bandannas or wearing small comales (similar to a fry-pan) like hats, their skin is whiter than ours, but they have long beards and the hair up to their ears.