New to all this...

I suppose "songwriting guidelines" can vary from "do what sounds good" to "it's gotta have this many verses, repeat the chorus that many times, and have a bridge after the second chorus."

There's a bunch of info around on songwriting, in books and websites and such. This earlier thread might be helpful:

http://www.absolutewrite.com/forums/showthread.php?t=99619

And here's something I've participated in:
http://fawm.org

The most important thing to remember when song writing is to write EVERYTHING that you come up with down straight away. Even if it doesnt fit the tone of that particular song, it may work in one in the future.

Also, listen to the bands that influence you the most and examine how they structure their songs. The arrangement in a 7-minute track from Machine Head will be very different to something written by Jack Johnson. Dont think that "borrowing" ideas from performers you like is ripping them off. They stole half of them in the first place lol

Great advice above. I'd say if you're looking for a basic template to start with for a rock song, you can use this:

Verse 1
Chorus
Verse 2
Chorus
Bridge or Solo
Verse 3
Chorus
Chorus

I totally agree with Severian about holding on to any scrap of music you write and using them later to mix and match. A heavy riff that you wrote as a chorus could be turned into a light verse in a different song and vice versa. Within a single song you want to have a steady meter, though so the song isn't totally disjointed.

In general, you want a song to either start small and build or to have an ebb and flow. In other words, don't play at the same level of intensity all the way through even if you're playing the same chords.

As far as writing lyrics, for a new songwriter, I'd recommend writing a full song's worth of music then adding lyrics (unless you have lyrics lying around you want to put to music). Once you have the music, you'll know the "feel" you're going for and you can craft lyrics around that, whether they're angry, moody, light, or whatever. Once you pick a lyrical theme, stick with it all the way through and don't try to do "too much". You can tell a story in 3 parts with the verses and repeat a "summation" as your chorus.

Most of all, trust your ear. Write what you enjoy. Some days it'll come naturally and some days it won't come together at all. Some songs you write you'll love at first and quickly grow tired of them, others you'll think are mediocre at first but they'll grow on you. Music's a living thing and writing songs doesn't cost a penny so try lots of things and enjoy it.