Plotz wanted to know how to express "try harder!" in Quenya. Tolkien demurred, and certainly gave it some thought!
Tolkien found the phrase rather problematic due to its idiomatic nature, and decided in the end to approach the simple phrase within the context "put forth effort," on the basis that "your first effort / former efforts did not succeed, now make another more determined / greater effort."
To quote Tolkien's notes in Parma Eldalamberon 17:
In Quenya, the imperative would be used. This with immediate time reference was expressed by á before the verb (occasionally after it, sometimes before and after for emphasis). The verb was in the simplest form also used for the uninflected 'aorist' without specific time reference past or present or future.
Harder must be expressed by 'with more/additional effort'. This will be done by a derivative of the same verb as that used in the imperative.
Thus using the augmentative prefix am- we arrive at the phrases above, highly contextual as you can see. Helge Fauskanger observed:
The form am- as such is in late Quenya only used before p and (presumably) before vowels; the longer form ama- came to be preferred before r and l; before other consonants, the prefix assumes the form an- (pronounced, but not in Romanized Quenya orthography written, añ- before c) (PE17:90-92). Phonologically we would expect am- before y- (since my is an acceptable Quenya combination); however, Tolkien used an- in the word anyára.
Translations in the same order:
Try harder (now)!
Look more attentively/closely!
Sing with more vigour or with more vocalic art!
Proceed with more determination!
Watch more closely!