The best writing is tight and spare.
This doesn't mean it can't be evocative and descriptive. Don't confuse descriptions, scene setting or any of the slower paced parts of your story with flabby writing or blubbery sentences.
What is flabby writing?
This can include unnecessary adverbs or adjectives, jargon or cliche, saying the same thing in different ways, or just simply overwriting - giving the reader too much information.
A few slimming tips
Reduce the number of adverbs by choosing more appropriate verbs. Adverb-laden writing is often lazy writing.
Get rid of adjectives that seem more like subjective opinion than objective description (unless you are writing in first person or close third person and are using these to tell us about the narrator's attitudes).
Some adjectives are meaningless fillers. What is the difference between exact same and same? Previously done and done?
Watch out for adverbs that are not providing information: very, really, totally, completely, extremely, decidedly.
What about sentence components such as "the fact that" or "as follows" or "one of the aspects"? Are they earning their keep?
What other ways can you think of for cutting back on flab.
Readers everywhere will be grateful