Beware of the ear cleaners if you go to Anjuna market! If anyone approaches you trying to stick something in your ear and comes up with something disgusting they say is from your ear, don't be fooled, it's a con. We heard of someone who parted with 3,000 rupees on the way into the market and had no money left to spend there!
Take a bottle of anti-bacterial hand gel with you to cleanse with on the beach or wherever - toilets don't always have soap. A loo roll or baby wipes are handy too for the beach and day trips.
Only drink bottled water and make sure the seal is not broken before opening and don't have ice in drinks unless you are certain it is from bottled water.
Power cuts are frequent, normally when you're in the flippin' shower or trying to do your make-up, so if you have room in your case, take a torch.
And for the ladies - don't wear high heels! You could easily break an ankle or worse wearing them over there.
And don't forget to barter in the markets - it's actually really good fun when you get into it!
I'm sure there's lots more I can't think of right now. Anyone got anymore?