The songwriter's mantra: Write. Record. Repeat.
Write. Record. Repeat. These three words should be on the mind of every songwriter who wants to make a career out of writing. Your music will never be heard if it is never written. Your songs can't be distributed unless they are committed to record. Your career won't make you money or get off the ground unless you repeat this process, over and over and over again. Write. Record. Repeat.
It is simple math -- the more songs you create, the better chance you have of one (or all) of your tunes getting noticed. After a while of habitual writing, you'll also start to notice your lyrics and melodies "mature." Your arrangements will be more refined, and listeners will take notice of your ability. This is the embodiment of learning your craft, paying your dues, and playing the odds. Write. Record. Repeat.
Don't let distractions or fear win. If you really have the goods and want the world to know, you have to keep creating. Write. Record. Repeat. On the train and feel a little silly singing into an iPhone? Pick up a songwriter's journal. Lyrics aren't the only thing that can be captured in word form. Example: "Song starts like 'Be My Baby' drum intro. Acoustic guitar joins with vocal V1. Add Rhodes and tamb V2. Blow up chorus with lush strings..." After a few scribbled notes, you might press record on your cell phone, too excited to let the idea escape, confidently letting everyone know you are a creator with an idea and proud of it.
If songwriting is a part of your core, this mantra will never produce a wasted moment. Art is within you and it needs to come out. Let it out, do what you love, and don't be afraid. It's all good. Write. Record. Repeat.