In today’s market multiple submissions are usually accepted by agents and editors. But read submission guidelines carefully. Some may say they want an exclusive right to read the manuscript. You need to be aware that before you grant this, you should ask how long it will take. You might even put a time limit on it. Because if an agent ties your book up for six months to a year and then turns it down, you start all over again. Try to send to all agents and editors who have no problem with multiple submissions. To me it indicates that they understand today’s market.
I'm a serious writer, meaning I have a regular daily writing habit, and I'm interested in sharing my work through publication. My favorite literary form is the novel. I write to entertain myself and my readers.