It's a good start. A cool way to start off with a song is composing on a piano (analog or electronic). Writing melodies on that is easier than the guitar, as you have easier access to all the notes, but you can always add upon it when you take it to the guitar itself. Striking up inspiration is as simple as listening to other songs, usually paying attention to nothing but the guitar. Above all else, when it's like a chore and it's too hard to write anything, take a break and try later. Writing music should flow easily without any problems, so it's a natural kind of thing. It should never be taken like a chore or if you're frustrated with it.