I learned over the years I can be my own worst enemy. The best example was about fourteen years ago one of the big bosses at my day job asked me if I knew of someone who would want my ex-boss's job? Dummy me, said, "No. I can't think of anyone." What I found out later was he wanted me to say, "Hey, how about me?"
Why he didn't just ask me straight out if I wanted the job, I'm not really sure. Maybe he wanted to see if I had the drive/ambition to move up into management. Whatever the reason, I know part of the reason I didn't say, "Hey, how about me?" was that I didn't have the self-confidence.
One of the good things (there are a few) about growing older is that you realize failing at something isn't the worst thing you can do. Not trying is.
So it's like riding a roller coaster for the first time. You're scared as you stand in line with your friends and family, trying not to show it while waiting for your turn. You watch everyone who gets out of the cars, they're laughing or smiling big even though they look crazy with their hair all topsy-turvy. Then you get your chance. You buckle up and before you know it the car is clinking along. You reach the top of the first hill and you look down the long drop. You inhale with an "Oh, crap!" or something worst and then the wind's in your hair and you're screaming and before you know it, you reach the bottom. Relieved. You're ready for the next hill and drop. They come fast, up and down, twisting and jerking you around but nothing like that first drop. The airtime your butt is off the seat takes your breath away. Yet it's so much fun. Before you know it, it's over and you realize it wasn't as bad as you had thought. If anything, you want to do it again. You're willing to take a chance again.
That's how to build self-confidence. One drop and hill at a time.
I'm going for the Kingda Ka roller coaster (world's tallest and fastest they claim). That's what trying to become published is to me. To try to do something bigger and scarier than anything else. So I continue to work hard on my writing and get my manuscripts out there. Whatever happens will not because I didn't try.