J.R.
they are pretty stretchy, so I use that to my advantage in getting them on straight.
I start at the limb tip end, and peel them down to the butt end a little at a time, straightening, and smoothing as I go.
Once I get to the butt end, I trim off the excess to the spot where I want them to terminate.
Then I use a box cutter blade (or sometimes my pocket knife if it is good & sharp), and carefully trim them to the shape of the limbs at about a 45 degree angle.
Once I have them trimmed to fit, I blacken the edges with a sharpie, then spray a couple coats of clear satin/flat on them. I like the Krylon indoor/outdoor stuff.
Rick