Wedding photography w/ Nikon D3000 tips?

I'm photographing a friend's wedding and reception and I'm looking for some tips. For example, this is my second wedding "gig" and at the first, I was scared to use to flash in fear of the dress getting too washed out in the photos, however I ended up regretting it. Should I use my build-in camera flash, or should I be looking for external flashes? And what about lenses and/or filters? What should I be considering?
Any help or tips would be much appreciated! I'm still new to the photography scene!

I do hope you're doing expectation management with that friend. Certainly if it's a paying gig.

An external flash is a must. The most important tool for a wedding photographer is the flash. You need to master direct, indirect, indoor and outdoor flash.

A decent lens will also help a lot. If I had to shoot a wedding I'd rent a nikon 24-70 f2.8

Yes, between now and the wedding you are going to have to master using your flash and stop being afraid of it or anything else having to do with photography.

I love the term, "expectations management". Perfect

Get an SB400 or SB600 with a diffuser. I'd recommend the inexpensive Stofen, or the more versatile Lumiquest or Gary Fong series. I have all three and find them to be game-changers when shooting flash portraits. My personal recommendation of flashes would be the discontinued (but still available) SB600, as it allows you to tilt the flash head horizontally or vertically.

For lenses, look at the 35mm f/1.8 as a relatively inexpensive low-light lens. This should give you very nice bokeh when taking available light photos, and is razor sharp for portraits.

Bring extra SD memory cards, all formated beforehand. Remember to make a list (with the input of your friends) of different group poses and situations that they want.

Finally, shoot often. Shoot multiples of each pose, as you never can tell when closed eyes, or something in the background ruins a great photo.

I've given up being the primary shooter at weddings, but have always offered to be the second photographer, capturing mood and candids.