When it cones to writing you can't force it.
Sorry, but this is simply not true. As with of all music/arts projects, the way I understand the thing, the ratio is always 5% Inspiration, and 95% perspiration.
That 5% can be anything from a riff, a song title, a melody, a lyrics line, some song you heard and thought "I gotta write a song with this kind of vibe".
To me, that's pretty much the only part you can't force out, but bear in mind it's only 5% of the total output.
Also, let's say you're killing time at a party or whatever where...KEEP AN EYE AND AN EAR OPEN FOR IDEAS. Always. It may be something catchy someone told you, or the music at the supermarket's radio, it really doesn't matter. Get your ideas in books or even on TV.
Ok, now let's say you got a new song title, what do you do now? Easy.
Go get your notebook where you write down all your music ideas, lyrics, etc [and if you don't have one, run to Dollarama to get one before I go kick your ass for only asking how to write a song!].
Get on a blank page, write your song title on top of the page, and just throw down words, ideas, lexical fields, whatever cross your mind. It doesn't have to rhyme or sound good at this point. Do that for 10-15 minutes, more if you feel you need more. Fill at least 3/4 of a page.
Then go do something else then come back and read it back. Any perticular words stand out? Got some similar sounding words? It doesn't have to necessarly rhyme at the end of the word, for example the words
distort and
destroy are similar sounding, yet they don't rhyme.
At this point you should have AT LEAST ONE idea for a line, or even an entire chorus if you're a bit lucky.
Then you can go in books or on the internet to get some quotes about your subject, a poem, existing lyrics, etc... go read that it may veeeery well spark an idea. I don't have to say the idea here is not to steal, but to get inspired.
Well, honestly I could go on and on about songwriting, but you see how it's done. It's everything but a divine touch mysteriously guiding your way into the glory of having wrote a great song, but a hard and meticulous craft at best. I would say there about 0% magic involved in the whole process of writing. It also goes the same if you start with a guitar riff or whatever, you got to explore all the avenues and let it all out. Of course, all your lyrics ideas neither your riffs are going to make the final cut, but if you force yourself to write 2 riffs a day, no matter what, there's a very good chance you'll have a song at the end of the week.
So, my advice is to take it one small bite at the time, and to get out of your head that because you have no "inspiration" you're stuck here without anything you can do. If you want to learn more about songwriting, there's a ton of resources on the internet, and if there's something you can't find you can ask me and I'll try to help you in the best way I can.
Happy writing.