I've got a nice top with a pattern similar to this one http://1.bp.blogspot.com/_npjnG8dYNgc/SYpNfXxT2FI/AAAAAAAAAIc/UZRE3MvImYI/s400/black+damask.jpg and I have no idea how to accessorize it for a friend's wedding.
Any ideas?

I would do so fun accessories in bold colors! Like a chunky necklace and earring set in Neon pink, or bright red. Something to give it a little color and make it POP! You could also make a brightly colored clutch/handbag! I'd suggest not overdoing it though, only a few colors and items. Such as-
A brightly colored handbag and heels
A chunky necklace with matching earrings and maybe a few bangles or a big ring.
A big ring with a chunky necklace

something like that :)
Here are some DIY and Ideas
http://dollarstorecrafts.com/2012/05/make-neon-drinking-straw-jewelry/
http://www.henryhappened.com/diy-turquoise-clay-necklace.html
http://transientexpression.com/neon-diy/

I'm with Pamela

You'll need to break up the print with some bright, large accessories

Go for eye-catching blues or pinks... if you're a little shy of wearing something so bold then go for gem tones which is colorful without being so bright

Just remember to balance every thing, like... if you're going to wear statement earrings go minimal or without a necklace (and vice versa), or if you put on a large cocktail ring don't wear heavy bangles on that same wrist.