Every natural language has a system of metaphorical usage that allows words to be used understandably when taken outside their literal meanings. Systems of metaphor in my experience differ between languages but remain strikingly similar to each other in basic ways, which suggests that they reflect something basic in human cognition. For example, all metaphor systems that I've seen or read about allow speakers to talk about time by using words that are about space—specific correspondences differ between languages, but the basic metaphor that time is space seems to be universal.

Ouxu also allows natural metaphor. But be careful, because metaphor is tricky in an artificial language. It's beyond my ability (and maybe anyone's) to specify a complete metaphor system for a language, and unless you are outstandingly self-aware and conscious of how metaphors work, when you use metaphor in Ouxu you will probably carry over assumptions willy-nilly from your native language. Therefore I designed Ouxu's vocabulary so that metaphor should never be necessary. You can always say what you need to literally.

Nevertheless, Ouxu would be unnatural if it didn't allow metaphor. To speak of time as if it were space, simply use a space-related word and inflect it with -hu (-time). The same goes for many other simple metaphors. Metaphors that are common across many languages are fair game: Associating the upward direction with higher social status, associating upstream locations with purity and downstream with contamination. Also good are many standard metaphors that have names, like personification (taking an idea or an inanimate object as person).

Pa husakufhu upinpotatsupe xagtugetsaepe.
Belief now+far+time morally-good+opposite+snake+exist predator+large+bird+exist.
Once upon a time, there lived a serpent and an eagle. (-far- is a space word)

Beyond that, use your common sense, and bear in mind that Ouxu is designed to display its own culture which stands far apart from any shared culture of English speakers, and from any natural culture that I know of. As a rule of thumb, maybe a novel metaphor is a good idea if it is simultaneously surprising (I hope that indicates that it's not stolen from another language) and easy to understand (I hope that indicates that it's natural).