I've wanted to write a song for someone for a long time. It's their birthday, and I want to make a special song for her. Any ideas on how to start? I play bass and I know how to read most music.

That depends. Is it for someone you like, or have liked or loved? or a family member? like a girlfriend vs a sister. I can certainly help you man but I need some more specifics.

umm, I'm sure there are better websites.

look here for learning how to make love songs/poetry.
http://www.homestarrunner.com/sbemail195.html


on a serious note, I think she might appreciate a cheesy poem instead. You got to be able to laugh at yourself.

if its a rap song i can definaly help

Try searching for poems and lyrics.

Bass isn't very good for writing music. Learn guitar or piano and write songs with that.
Have you ever written a song before?

What I usually do is just dick around until something sounds cool. Also, I'll use my knowledge of music theory and chords and stuff to figure out what would sound decent.