Any grammatical errors A life spent making mistakes is not only more honorable but useful than a doing nothing?

* "than a doing nothing" should be "than doing nothing". The "a" is unnecessary.

* "more honorable" and "useful" are in the wrong order. Logically, it's better to say "useful and more honorable".

Here's the corrected sentence:

A life spent making mistakes is not only more useful but also more honorable than doing nothing.