What I do is just mess around on my uke, guitar, or piano until I find something that sounds cool and I build off of that. Usually I create the melody before even touching lyrics. When you write lyrics it's good to have a concept, then decide a vehicle your song will go off of (extended metaphor, story, emotions), how will you convey the idea. (The less literal you are, the deeper the song will be). A lot of people make the mistake of waiting for inspiration, or they want the song to mean something to them before they write it. Do not fall into this trap, if there are emotions you want to convey that you aren't feeling try it anyway. As the song develops it will become more convincing. At first, don't worry about rhymes, try writing your idea in prose (non-poetic speech) and developing your rhymes from that. Figure out when you want to reveal parts of the story, for example (V1: you left me V2: I feel alone C: You're better off now V3: I can move on, or try telling the story another way (V1: I can move C: You're better off now V2: But i still feel alone V3: Ever since you left me C: You're better off now). When you have a concept for each verse and paragraph, then start writing the song, with rhymes and such (don't get too caught up in perfect rhymes. Slant rhymes, assonance, or even not rhyming is perfectly fine). Sometimes a few lines will just come to you, work with those and use them to develop a concept. But ultimately, just try. It doesn't matter what system you use. You get better with practice. My first songs were shallow, the rhymes were terrible... they just sucked. Now I can write things I am actually proud of, ones ill look back on as milestones. If you take nothing away from this but just one idea, then take this. Just Write