What is it about her that has you so mesmerized? List the things about her that make you feel the way you do,and be honest and sincere! Then tell her in a song! Do you like her hair? If so, why? Do you like her smile? Her eyes? The things she says to you? Tell her what it is that you love about her so much, and do it in a tasteful manner. Just tell her!

fred has one approach, another could be this:

talk about you and your life and what its like when she is not around, and what she does to you, and why she is the difference etc. personally i think love songs where the message is subtle are best, but thats just my opinion.

There were so many girls that I liked, but I didn't have the guts to say what I feel. Now I often think..what if. If I had told them, they might have laughed at me, or whatever, but I wouldn't be wondering what if today. I would know. There were a few girls that carved me up when I told them how I felt, but there were a few that I was sure would, and didn't. I wound up marrying one. Zoo is right, there is more than one way, and sometimes being subtle is best, or could be used as another approach. I feel for you pal, I really do! But if you try the subtle approach, and it doesn't work, just make sure she knows how much she means to you. It will be painful if it doesn't work out, but you'll have one thing in your corner with either approach...you tried!

#1 Girls like guys who play guitar. So thats a plus for you already.
#2 Even if you write a terrible song odds are in your favor that your girlfriend will like it and love you for it simply because you wrote it for her.
#3 Check out that song in the movie wedding singer. The song at the end that Adam Sandler sings to Drew Berrymore on the airplane. Most of the things he sings about are trivial things. So the lesson is you don't have to write the worlds deepest lyrics. It's ok to keep it simple.

JTC is right. however, simplicity doesn't mean ordinary. so avoid any "cliches" as much as possible - make it yours not "factory" made one.

think of all the places you went with her - things u did, food you ate, all those little things add up and those are the things that make your song unique.

when i say cliches, i mean all those things that has been said and done before - i love you till i die. you take my breath away, oh i can't live without you......we get the point that you love this girl....now tell us when, where, who, what, how, why you love this girl.

one more thing....BE HONEST....you don't have to look at other lyrics to see what they wrote - you can check out other lyrics for like rhyme and song structure references. but it's your song. write what you wanna write.

good luck man!

Don't forget to say in the lyrics that SHE is unique in the whole world.
SHE is the special one. Remember that ;)