A guidebook for the area would be useful for you. But you can also look at the regional and local tourist office websites for ideas about what to see and do:
The closest WWI sites near Reims are The Chemin des Dames (south of Laon) and the Bellau Woods area and nearby cemeteries and memorials (just outside Château-Thierry, though there are cemeteries and memorials scattered throughout the region.
There's more info on the Château-Thierry tourist website about the WWI sites in the area.
I wrote a photo report about visiting the area between Château-Thierry and Laon and it includes the Chemin des Dames, if you want to have a look: http://tinyurl.com/cr52tkf
The most well known battlefield sites are north of Reims in The Somme in the area of Arras and Amiens:
Make sure you get good maps and I like the Michelin maps. You can buy the Michelin maps from their website and here is a link to the page that shows you the 1:200,000 scale maps of France: http://tinyurl.com/4bt96ev
And here is a link to the page that shows you the 1:150,000 scale maps of France:
A nice feature of the 1:150,000 maps is they show the starred attractions in the corresponding Michelin Green guidebooks. The Michelin maps have icons for all kinds of historically/touristically interesting things such as châteaux, ruins, churches, abbeys, scenic view points, caves, Roman sites, megaliths, designated scenic roads and many other things. Usually when I'm exploring various regions in France I just look at the map and I am able to plan interesting and scenic drives just reading the map. For instance, I usually look for a designated scenic road, which are highlighted in green, and I especially look for towns with the historic church and/or château icon. I also try to make sure the route goes through as many small villages as possible. Usually putting all these things together I find interesting and scenic drives without even knowing where I am going and with no assistance from a guide book.