There's no such thing as a perfect song. If this is your ultimate musical goal, then put down your guitar, pen, and paper, and find yourself a goal that you can actually achieve in your lifetime. Songs are mostly written from life experiences, and since life isn't perfect, then your songs about life have little chance of being perfect either.
I've written more songs than I can count, and the songs folks seem to love the most weren't written with perfection in mind. They were songs written from the heart very quickly, and with little attention to finding the perfect rhyme, melody, or hook. Songwriting is all about communication, no matter what theme or genre you choose to write about. Remember the old saying, "beauty is in the eye of the beholder"? No matter how perfect your song may sound to you, it may sound like complete garbage to someone else.
Would you settle for a guide to writing great songs? That's a goal you can actually achieve, if you're willing to put in the time. There are many things you can do to write better songs. The first of these is to become a good listener. Learn from the songs already written that you really like; then relax, and write down what you feel, no matter if it rhymes or not. When you have all of your ideas down, then start forming your rough sketch into a song.
The more you practice, the better songwriter you'll become. Write songs that mean something to you, and then let others decide if your song is good or not. For every hit song a songwriter writes, there are a whole pile of songs they've written that most of the world will never hear.
I can tell you where to find a song that's almost perfect; just be in the delivery room when a baby comes into this world, and listen to it's first cry. That's about as perfect as a song gets in this world!