I must agree with writing 3-4 screenplays a year. Ideally more if you can, think about it. After several years if you've written 5 per year that'll give you 35 projects. You can then choose maybe 3/4 of those projects to concentrate on while working on others.
Don't put all your eggs in one basket and just write 1-3 screenplays. The larger the body of work you have (portfolio), you'll give yourself a much better chance of someone liking something you have. Or they may not like the projects necessarily but they may admire your style of writing and work ethic and thus give you the opportunity to write something for them. And get paid for it.
If you want a career in writing then you must write. Build up that body of work. The harder you work and the more you write, the more luck you'll create for yourself and sooner or later someone will sit up and take notice of you.
Be persistent and never give up.