Now then: in the publishing world, there are very often scenarios in which what would otherwise be a great idea is actually a terrible idea due to one or two crucial detail(s). As part of your (and, frankly, my) continued education in this industry, I present to you the following examples:
Good Idea: Venting to your friend, spouse, significant other, &c about a negative review of your book.
Bad Idea: Venting to Twitter, Facebook, the Internet at large, &c about a negative review of your book.
Good Idea: Following an agent's guidelines when submitting your novel.
Bad Idea: Following an agent to his or her office/car/home to submit your novel.
Good Idea: Reading industry blogs to improve your writing and querying.
Bad Idea: Reading industry blogs instead of writing or querying.
Good Idea: Selling yourself in order to promote your novel.
Bad Idea: Literally selling yourself in order to promote your novel.
Good Idea: Setting aside a specified block of time to write each day.
Bad Idea: Setting aside your family, friends, and day job to write each day. (May lead to the above scenario.)
Feel free to create your own good idea/bad idea in the comments!