Few writers use parenthetical statements well. For most of us, they're usually a gateway to bad writing. Here's why:
1) They distract. In every sentence you write, you must decide what gets primacy in the readers' mind. A secondary, parenthetical thought is likely to subvert your main idea rather than amplify it.
2) Some thoughts are too important to put in parentheses. Don't let a good idea just fly past your readers' heads. Give it a sentence of its own.
3) Likewise, if something is an aside, put it aside. Refer to it elsewhere in your piece and stay on point with your readers. Use an asterisk or a footnote so your reader can stay with the primary thought, and then explore your parenthetical thought later.
4) They make your sentences too long. Don't help your reader forget your real idea as they plow through your parenthetical idea.
I'll allow one exception: one word parentheticals can work if they're used quickly, self-effacingly or with irony:
Vegetarians often presume (wrongly) that they can convince people to give up their meat.
The bottom line: kill off most of your parenthetical statements. Your job as a writer is to organize your thoughts, not drag your reader along as you flit from idea to idea.