Are you set to make a song? I'm going to touch on three points on what it takes to make a song from top to bottom.
First off come up with the song title for your song. A song title can do a good deal in making what that song will be about musically and lyrically early on which can make your job less complicated moving for work. Certain titles are better than others, of course. For example, you might take into account coming up with a song name which suggests some sort of back story which can make coming up with the topic and subject matter of that tune lyrically much easier. On the other hand you can also come up with a theme rich title which exudes a particular feeling which that song will possess.
Also, once we get our song title we can come up with our initial hook. This is the most challenging element of writing a song because the most difficult part of a lot of things is getting started. How we do this when we are going to make a song is to take our title and try throwing different notes at each word and syllable in that title.
Different combinations such as stretching notes over numerous syllables or going staccato and assigning one note per syllable or even numerous notes per each syllable works to give you a lot of different ideas to work with. To further complicate things and give you more options, work with putting different chord progressions within the key you're working in all around that melody you have come up with. Different progressions can drastically modification the effect and efficacy of that hook. Remember that a strong hook is equal parts the melody as well as the support around it which involves the progression and the instrumentation.
Once you've your initial hook it becomes far less difficult to branch out in either direction to make up the rest of the tune. There is nobody perfect tune structure, so don't bind yourself to a particular verse chorus verse chorus formula. Often times the best and most interesting tracks are those which make a lot of interesting changes and to deviate from the standard structure.
Lastly, writing lyrics can be the most challenging element for some people. The good news is that starting out with the music makes writing lyrics that a great deal less difficult because we already get some idea as we come up with every bit musically the kind of rhyming or timing structure we need to stick to. Then, after you come up with your initial line for a particular section of your tune, you know the rhyming structure and will stick to that which narrows down the kinds of rhymes you are going to be searching to use. While it seems like it's limiting you and constricting you, in reality you'll have much more done because you be a lot more focused and writing.
As I have only scratched the surface so far, I suggest that you refer to my complete resource on songwriting, "How to Write a Song - The No BS Songwriter's Bible" as this covers every element of songwriting from top to bottom as well as dozens of tips and tricks which you can use to successfully jump start the songwriting procedure and force musical hook ideas to come to you.