I know from experience that rejections come far more often than acceptances, so I guess I ready myself for it. This way I'm not as disappointed with a rejection and ecstatic when it actually is an acceptance.
1.) Tell your family and friends how you feel and they'll boost you right back up-at least for a little while. My husband and two girls lecture me when I become pessimistic and remind me of how far I've come.
2.) Do remember what you've accomplished thus far. Maybe you've finished your first short story or novel, or that first piece is published. Both are great accomplishments and stepping stones to more successful moves in the future.
3.) Keep writing! Even if you feel you've written crap. Write out the story and get it down. You can go back over it and edit it as much as you want. I've had first drafts waiting years for me to come back and revise, and when I read over them again new ideas come to mind that improve the story.
4.) Keep sending out submissions. Remember what one editor may hate, another may love. This has happened to me in the past. Everyone has an opinion and a preference and many times they differ vastly.
I plant continue writing and sending out submissions, even though I get nervous and negative thoughts race around my brain while awaiting responses. I guess this is something writers must endure if they want to succeed.
Keep Writing and Happy Reading!