You need three things to write a song: music, lyrics, and passion. Every guitarist can make music, and passion is something your born with, but the lyrics play a huge part in a song. They can make or break a song. Before we even start, here are two basic guidelines to think about. Just a reminder, that these are not rules that have to be followed. I'm simply expressing my way of writing lyrics.
1. Do not expect perfection your first time. The first set of lyrics is going to not to great. Face that it will happen and don't get upset over it.
2. Don't force yourself to rhyme. If you have to search on the internet words that rhyme with another word, then it won't work out. Don't make up new lines just to rhyme. Rhyming will destroy your song if you stress over. Just write what makes sense and go with it.
Now your ready to start on your lyrics. The first thing to do is to find an inspiration. Your inspiration sets the tone of the song and should correspond with the beat. Inspiration could be anything. The most common is love. However, if all you write about is love and break ups, your missing out so here are some more ideas. Annoyance (Telephone), Choices (Should I Stay or Should I Go), or Freedom (My Life) are all good inspiration. Also, everyone loves a good peace song (One Day; We are the World).
Next, fill yourself up with your inspiration. Focus almost every thought into the emotion. Then, find a metaphor or a phrase that describes or corresponds with your feelings. Metaphors are a big part of lyrics. Popular songs don't just say we're going to party or You broke my heart. They say we're gonna light it up like its Dynamite or Shot in the Heart and your to blame. Using this helps to get your point across while not boring your audience. Remember that you don't have to explain your inspiration you just have to show it.
I find it easiest to then start the chorus. Take your basic metaphor and just start fitting it into you music. Slowly piece by piece, begin putting bits into place. Bear in mind that this is just the first draft. Now is the time when you want to just dump everything you have in your head onto the paper. Don't stress over getting lines right. Just put anything down that comes into your head.
I also find it easy to make more verses than you'll need. This comes in handy during editing. You'll be able to pick the ones you like best and not have to cram things in. If you're having trouble with verses, then sit down and work more on the music. The more you play it, the more you will have ideas on what goes with it.
Now that you have a basic draft, go back over and remove any lines that don't fit our your not comfortable saying. Keep it comfortable or you won't get a song you'll want to play. An uncomfortable song to the writer will be more uncomfortable to the audience. Keep reviewing and revising. The show it to a friend or band member. Have them come up with additional verses or lines. A band relies on all members for lyrics and music not just a designated songwriter.
You'll find that this way will get you more songs than you need. It is one of the few ways that people can actually sit down and say, I'm going to write a song. Just keep going over your song until your happy with it and soon you'll have a hit.