Lots of great advice here. I'll skip my magnifier advice as that's been well covered.
Clover Fork Pins. I would never match up seams without them.
I have a very hard time with dark fabrics. I can't see anything well if a dark fabric is involved. Contrasting thread and pencil-thick markings vanish.
I use a pounce pad for outlining templates and stencils on dark fabrics.
I haven't found a decent marker for dark fabrics and white/silver pencils don't work for me at all. Need a thick marker.