Stop with the food please - I have to wait until October before I am out there again and I've drooled all over the keyboard. The coffee is excellent if you like strong and dark. Bintang beer is the best.
First time? At the airport make sure you have your entry visa money handy, and exactly right. Mosquito repellent - goes without saying. If you get the chance to look at a fish book, do some homework. Those critters at Lembeh are so strange that it helps to prepare, otherwise you can be staring at apparently nothing for ages until it comes into focus - and then you don't have a clue what it is. A hint of recognition helps to appreciate things better/quicker. Night dives are good/brilliant and well worth the effort. Ask for mandarin fish. The guides in Lembeh are amongst the very best in the world, they love to be asked questions, given challenges, your interest will be hugely appreciated..
A side trip to Tangkoko to see the tarsiers is worth the day off if you like to see other animals.