I'm pretty much a beginner, but I'm getting pretty good at guitar. The thing is I'm having trouble starting up a band and/or writing songs. Any tips are helpful.
What I do is sit down with an idea or sometimes just from boredom, and play till I come up with an idea. Do you write any lyrics or poems? Usually it's easier to add music to lyrics - but that's just my opinion. Hope it helps.
I keep trying to write lyrics, but when it comes to the riffs I'm always at a standstill.
Do you mean, writing songs as in lyrics or melodies, or both together? Dude, its arguable, lots of people will say learn the theory it will greatly help improve your songwriting skills, alot of people will say, GOOD music will just come to you and you should feel it out.

It's totally up to you how you want to write your own songs. I reccommend studying up on songwriting and just picking up a few techniques so instead of just writing riffs you can get a full song down, this makes it much easier too add lyrics to.

Then again, sometimes if a melody comes to me, what i do is sing into a guitar tuner to find the notes im thinking of. I'll locate those notes on the fretboard or keyboard or whatever, and then build on that and see what sounds good, other times ill go and find the key, muck around and vary up the scales over what progression im playing. Lets say you have something in the key of D , you think hmm, find some scales you could use over it, for instance d major, then vary up the ntoes of that scale over the progression.

For things like writing lyrics, i suggest, ( as emo as it sounds) writing down a few words that your feeling at the time, try channelling what you feel into lyrics, say you just found your girlfriend in bed with another women you could write a draft.

Betrayed, cheated, frustrated,confused. Then turn that into something, doing this will also help out with the context of the song, the use of emotionalally effective words like this often helps to create the atmosphere of the song. Try and fit that into a sentence now.
Yeah man, well it comes down to personal preference. If you want to try and make it so people can relate to it then go for it, if youd rather it be personal than go for it, unless its what your aiming for, don't write for an audience, write music that expresses yourself, that being said, if you want to get the kiddies jumpin then write to the crowd.