Depends on what you want to reach for an audience - brief rundown:
The north of NH is probably the highest vote-getting total for him, and he just came from there, so you'd be striking while the iron is hot. Best subject: Low tax stuff. Don't be afraid to say "END the Income Tax." - We are the last state in the uniion with neither a sales nor income tax and even our Dems are afraid to support any broadbased tax. Towns: Berlin, Littleton, Bethlehem.
Southeast: The most Bostonized of the areas of NH, Romney has some support there, but the advantage we have there is that it is also one of the heaviest anti-war areas of the state. Subject: Romney will continue the war. Ron will end it. Cites: Dover, Portsmouth, Rye (Big bucks!).
Central: The most urban part of NH - You might think this area would be liberal, but the Rs just won mayorships in Manchester and Nashua this month. Subject: Probably a hodgepodge. I'd probably go there if I had a combo of anti-tax and anti-war stuff. Cities: Nashua, Manchester, Concord.
Southwest: Probably our largest, most untapped market. HEAVY HEAVY Anti-war area. Also one of the most liberal area in the state. But also surprisingly libertarian friendly: L(l)ibertarian candidates, even in open party races, always get 10-15% there and that number is up to about 25% now since the FSP move began. Really good volunteer base there as well (nhfree.org). Subject: If you have a trailerload of anti-war Ron Paul slim jims to dump, this is the place to do it: City: Keene.
Most cities (with the exception of Manchester, somewhat) in NH have very lively mainstreeets. Also, since the street is public property, you could canvass up and down Main Sts. all day long w/o getting kicked out. That's what I have done before and it works pretty well.
Hope that helps!
JM