Quite surprisingly I am shooting a Diwali event tomorrow (learned about it today).  It's sort of inofficial and I am not being paid for it but I would still like to do a good job (obviously).  It's indoors and I don't know the location.  I'll pack my Speedlight, my 85 mm f1/8 and my IS long lense and could use a few good hints, tips and tricks for the more experienced among you.
Thanks,

Tina

what is Diwali?

what type of camera do you have?

I would suggest bumping up the ISO quite a bit.  On the micros we get used to thinking that ANY noise is horrible and it is to avoid at all costs - but blurry pictures are worse.  A tripod is also very helpful even if you are moving the lens around a lot.  Having the tripod head 'loose' still provides quite a bit of stability.

With almost any event you will need a wide angle lens. I'm assuming you are shooting 35mm so you're probably going to want to bring along another lens.