The selvage sides should line up together. The fold in in the center. Cut away your selvages before you cut your strips or anything, It saves time. the threads that run paralle to the selvage edges are called the warp threads and are the strongest.They are what is called the grain. The threads that run perpendicular to the selvages are called the weft threads. You can remember this easily by remembering "weft to right". These threads can be weaker and should not be considered cutting on the grain, they are the crossgrain. If you are cutting on the diagonal then you are cutting at a 45 degree angle to the warp and weft which is called the bias.
warp = grain, weft = crossgrain, bias = 45 degree diagonal of warp and weft
When cutting strips I cut on the weft by placing the fold on a cutting line and using a 24" ruler, cut in 2 1/2" long strips that will be approximately 42" long each.