As any writer who has submitted his or her work for publication knows, rejection is a huge part of the process. Most of us have received more rejections from agents and/or publishers than we care to admit.
The first thing I share with someone who's contemplating submitting their manuscript for consideration for publication is to develop a thick skin. This can be hard because, in my experience, most writers are sensitive souls and being told your manuscript doesn't measure up can lead to days of self-doubt and despair. If you aren't able to develop that thick skin, it can destroy any pleasure you get from writing. I had one friend who would be depressed for days after receiving a rejection letter. She finally stopped writing all together which is too bad because she had a way with words that was almost lyrical.
The next thing I share is that there is a lot of luck involved. I do believe that a lot of getting published is having your manuscript land on the right desk at the right time. Of course, you have to have written the very best book that you can to start with. Throwing a story together and sending it out is all but guaranteeing rejection.
Another thing I always try to share is to remember reading is so very subjective that while one agent or editor may not like the story, another may love it. When you get a rejection, try to remember that it's only one person's opinion on any given day. Don't get discouraged.
The final thing I share is that there are different types of rejections. There's the form rejection which most authors hate the most. (I know I do.) There's the "Sorry your work doesn't meet our needs at this time" which isn't necessarily a bad rejection, it just means they've either already contracted a number of similar stories or they've stopped accepting your specific genre or sub-genre for a time. One of the better types of rejection is where they reject the story you've submitted, but ask you to submit something else you've written. This means they like your voice or style or sense of humor. There's something in your writing that they're interested in seeing more of. The best type of rejection is where they ask for revisions and have you resubmit the manuscript.
Don't let rejection letters keep you from reaching for your dreams no matter how many you may receive. Some of the most well-known authors were rejected hundreds of times.