Keep It Simple. Never forget the fact that the less is always the more. When you're making music, you like to show off what kind of complex chords progression or complicated melodies you can do that except yourself and maybe Mozart, nobody else is capable of performing or singing them! That is exactly where you're wrong. Look at the majority of big hits especially the ones that were the debut of entering a new writer in the industry, you'd realize most of these songs have ridiculously easy and memorable melodies, chords and even the arrangement. Listen to that solo guitar or that intro piano melody. How simple are them? This simplicity might be the most important key for a song to be memorable (of course only from songwriting point of view. The production and performance quality are not in our consideration here). One of the key elements for a popular song is that every one can easily sing along to it and possibly perform it. Each time your song is being covered, there is a chance for it to get more popular. Bare in mind that huge percentage of cover musicians might not be as musically trained as you are, yet them, covering your song can contribute a lot to your song to become more popular! So, simply make it the way they can cover it, and listeners can sing along!
Keeping It Balanced. The balance is super important element in a song. When we are talking about balance, we are referring to the amount of complications in each part of the song. For example, if your verse is very crowded or melodically it's too complicated with lots of up and downs, you would want to keep your chorus simpler and let your listener to breath and give a short rest to their brain to process what just happened in the complicated verse. Of course they might not know it but their brain is processing it in the background. Or on the other hand your verse might be not crowded at all and all (or most) of the notes are pretty draggy, then you'd need to create the hype in your chorus. Make it big. Make it punchy. Make it sound as if it's the climax of your song. Make it the way that wakes your listener up, and let it be like a snap to them, saying “hey focus on this song”. And then again cool down in the next verse.
This balance will keep your listener interested in keep listening and looking forward for the next phase and the next changes. These up and downs will keep your song away from being “flat” (of course not musically, but the mood) and that makes it more memorable for the listener. This way they will keep listening to it over and over, because psychologically, humans tend to enjoy these changes in level of excitement.
Tip. This one is another great tip I learned from those very few interviews of Max Martin and I applied it on my music, well, because I trust the man! It is to never introduce so many sounds at the same time. This one has nothing to do with the writing process and it's more about the arrangement and production but look at your music as a movie and look at your sounds and instruments as the characters of this movie. You should never introduce more than one or 2 (if they're from the same instrumentation family) at once. Bring in one sound, let it go for a few bars. Let your listener to understand and digest this new sound, then introduce the next one. Like this your listener wouldn't feel overwhelmed and also your song keeps being interesting because it will have more elements to introduce as the time is going by, and again, subconsciously your listeners will keep listening and looking forward to see what happened next.