“Write shorter epigrams,” is your advice.
Yet you write nothing, Velox. How concise!

[Scribere me quereris, Velox, epigrammata longa.
Ipse nihil scribis: tu breviora facis.]

Martial (AD c.39-c.103) Spanish Roman poet, satirist, epigrammatist [Marcus Valerius Martialis]
Epigrams [Epigrammata], Book 1, epigram 110 (1.110) [tr. McLean (2014)]
    (Source)

"To Velox." (Source (Latin)). Alternate translations:

Velox complains my epigrams are long,
When he writes none: he sings a shorter song.
[tr. Fletcher (c. 1650)]

You say my epigrams, Velox, too long are:
You nothing write; sure yours are shorter far.
[tr. Wright (1663)]

Of my long epigrams, you, Swift, complain;
And nothing write: I laud your shorter strain.
[tr. Elphinston (1782), Book 12, ep. 16, "To Velox, or Swift"]

You complain, Velox, that the epigrams which I write are long. You yourself write nothing; your attempts are shorter.
[tr. Bohn's Classical (1859)]

You complain, Velox, that I write long epigrams, you yourself write nothing. Yours are shorter.
[tr. Ker (1919)]

"Such lengthy epigrams," you say, "affright one."
True, yours are shorter, for you never write one.
[tr. Pott & Wright (1921)]

You say I write lines longer than I ought?
It's true your lines are shorter -- they are nought.
[tr. Wills (2007)]

You say my epigrams are too long.
Yours are shorter.
You write nothing.
[tr. Kennelly (2008), "Nothing"]

Swifty, you moan that I write long epigrams. You aren't writing anything yourself; is that you making shorter ones?
[tr. Nisbet (2015)]

My epigrams are word, you've complained;
But you write nothing. Yours are more restrained.
[tr. O'Connell]

“Much too long” you say, Velox, censorious,
Of my epigrams -- that’s quite uproarious.
You write none. Your brevity is glorious.
[tr. Schmidgall (2001)]

You call my epigrams verbose and lacking in concision
while you yourself write nothing. Wise decision.
[tr. Clark, "Short Enough?"]