Try repeating single-note riffs like the ones in "Welcome to the Jungle" and "Paradise City" (Appetite for Destruction). In their early days, Guns N' Roses used this kind of guitar work to keep their anthems moving.
Rip through pentatonic scales. These five-note patterns are the basis for a lot of Slash's awe-inspiring solos on tracks like "Sweet Child of Mine" (Appetite) and "November Rain" (Use your Illusion). You can hear a melodic quality in Slash's solos; they're not just a random collection of notes, and it's that well-tuned guitar sound that helped push the band into the big time.
Try some of the softer, minor-kay chord progressions on some of the "Use Your Illusion" tracks. Songs like "Don't Cry" have the distinct melancholy sound with Dmin-Amin open chord changes that sound good on an acoustic guitar.
Try picking a chord for a melodic sound. Listen to "Civil War" (another Use your Illusion track) for an example of picked chords. Note the Emin-Amin chord progression at the beginning of the song. The double disc has several tracks that show the musical development of the band over time, where "Appetite" relies more on a classic rock vibe and the guitar genius of Slash.
Get your G'N'R vocal groove on. It's not a Guns N Roses tune without the over-the-top wailing style of crooner Axl Rose. Lay down guitar work that works with a Rose voice to really capture the rock and roll qualities of the long-lasting glam-rock band.