Who am I to give such advice, you might ask, seeing that agent representation has, so far, eluded me. Nevertheless, in self-published books, and in writing forums relative to work submitted for critique, I've seen so many basic errors that my two cents couldn't possibly hurt the novice and might possibly help. So, as a writer, like me, have you at times been guilty of any of these?
Too many words ending in 'ly' - Excessive adverb use
Using a variety of speech tags when a simple, he said, would be better
Not using sufficient speech tags - Confusion about who is speaking
Failing to use separate paragraphs for each speaker
Too much telling as opposed to showing
Inconsistent POV (Point of View) - Whose head is the narrator in?
Inconsistent tense
Poor grammar or punctuation - Peruse reference texts
Multiple exclamation points or question marks - shouting
Too much backstory in one place. Break it up within the novel
Use of cliches or trite expressions - defines you as a novice
Repeating the same word on a page multiple times
Failure to continue building tension as your novel progresses
Loss of continuity, or failure to resolve all conflicts - Reader is left hanging
Not providing reader sufficient reason to sympathize with the protagonist
Although many other types of writer errors exist, if just these above were eliminated from your manuscript, then you are definitely on your way to representation.