R.
I've been playing 7 string for about 8 years now. The 7th string is an added low B. So, say for instance when you normally play and open D chord on your 6, now you want to beef things up a bit on that 3rd verse after the solo, take it down and octave & play a Low D by fretting the 7th string at the 3rd fret & doing a normal power chord.
That's how I made the transition. I started playing the 7 string just like a six, ignoring the 7th string until I got familiar with the wider neck and added string, then I started incorporating it into my songs that were written and recorded on the 6 string. Once I got to where it just felt natural to be on a 7 string all the time, I started writing more from the 7 string. It does take a bit of adapting, but one thing that I love about the 7 string that you do not get by simply tuning down is the added range, rather than transposed. It's not necessarilly for Dropped D as we know it. That requires tuning one string differently. This is added range.
I feel as comfortable and natural on a 7 string as I do a 6 string. I use it for a variety of styles too, so dismiss those misnomers about it's only good for music like Korn or Dream Theater. Think of it as adding 5 extra notes to your existing guitar, because that's really what it is about.