Think of some words that rhyme
Comes in useful when trying to write the lyrics
Don't think of words then a melody or vice versa
These need to be done together at the same time, if you have a good idea for lyrics or a melody write it down, but make sure when writing properly, you do both at the same time.
Do not come up with a title first
I don't know why but this seems to be a very popular tip among a lot of tutorials I have read/seen and I disagree with this one completely. It's important to make sure that your song has a theme/themes of some sort, but that doesn't mean one of them has to become your title. The title should be the thing that you think of last after you have all of your lyrics so that you can pick what's most relevant to your song.
Do something creative
Before attempting to write, try and do something creative or listen to some other ideas so that you know what you can say or sing about.
Song writing isn't always an easy thing to do, so try your best, and if at first you don't succeed, take a break and try again later.
Hope this helps