Begin with a capital letter. That’s always the best way to begin. Capitals are big and proud, they shout I’m here! I’m starting a sentence! to anyone in earshot.
Follow the capital up with a couple of lowercase letters, so that it doesn’t forget where it came from. Capitals do that sometimes, they can forget that they once were little letters too.
Sprinkle in some spaces, but not too many, or they’ll think you’re getting desperate. Add a comma or two, if you’d like; they don’t really matter in the scheme of things. They’re just pawns in the game, really. (Don’t tell them I said that.)
End the sentence with something really flashy, like a period or a question mark. Don’t use exclamation points, they make you look desperate (cf. the Capital’s shouts, above). If you’re really feeling adventurous, you can end it with a semicolon; just make sure the two sentences you’re marrying like each other. They’ll get in a fight otherwise.
Step back. Take a look at your sentence. Admire it the way an immigrant admires their new country rising up from the horizon. Admire it the way a taxi cab might admire a ferry.
Then, tear it down. You don’t owe it anything, that sentence. What did it give you but grief? Let it know what you really think about it. Words. Words are lies, all of them, every single one.
Tell yourself this as you kneel down to face the mess you’ve made. Pick up the broken pieces, the dangling participles, the split infinitives, and put them back together, gently, carefully. Breathe that thing back to life like God breathing Adam.
When it’s standing again, looking at you wordlessly, not trusting, get down on its level. Say to it, You’re your own sentence now. Turn it around and let it go out on its own. It’s not yours any more.
Start another one. This time, include the word serendipitous.