Never use WD40 on your sewing machine. It has a solvent in it. Never use anything other than sewing machine oil. Sewing machine oil is lighter in viscosity than many other oils. If you use a different oil, it could gum up your machine.
If you are sewing by hand and your needle gets dull, try running the tip of it across an emery board (fingernail file) several times to sharpen it. For those of you who don't know, the strawberry found hanging off traditional pincushions is filled with emery, and sharpening your pins and needles is what it is intended for.
There are a lot of good tips on this thread. I especially like the one about cutting through sandpaper to sharpen scissors.