I am making my own wedding invitations and was thinking of buying 8.5x11 sheets and cutting them into 5x7. I am planning on buying Crane Lettrra 220lb. Are there any special instructions for cutting these types of papers?
What do you advise?

I would offer a special instruction! If you are using a guillotine paper cutter, cut the paper in very small lifts, just a few sheets at a time, especially if you have a dull blade, and make sure the paper has chipboard underneath and above (several sheets) to protect the paper from the clamp pressure, which needs to be quite high with these cotton papers. If you do not clamp the paper tightly enough, a less-than-perfectly sharp blade with draw the sheets during the cut and you will get a sloping cut and unevenly-sized pieces of paper.

If you're just cutting with an x-acto blade, just make sure to make several light cuts with a sharp blade, preferably using a cork-backed ruler held down firmly. Use a cutting mat, if you have one.