Tawau is a town on east side of Sabah. From Kota Kinabalu you can take a 45 minutes flight to Tawau Airport. From the airport take a taxi for 30 minutes ride to Tawau. There are plenty of hotels in Tawau but I stayed in Hotel Emas. 
If you need Internet access, Sedap corner has free wifi. Its only 3 minutes walk from hotel emas. Ask the counter staff and they will show it to you. The food is good, the girls are pretty and friendly. If you are lucky you can also ask them out for dinner at the same time ask her to show you around town before you show her around your hotel room :).
From Tawau I went to Semporna. The journey took about 1 hour. At Semporna you can take a boat to go island tour. Go to the Jeti, beside the entry to Dragon Inn there a lot of small challet. Those are offices for tour and boat operators. Ask around and you can get good price for island tour. There are also diving packages there. Maybe you can dive Sipadan, Mabul and Kapalai. In Semporna there are lots of hotels. Dragon inn is a good one. As for pub and karaoke there are plenty. Food?? Lots of food here. Seafood especially. For me I dont like to stay in Semporna coz its too small with nothing to do at night except going to the pub one after another.
My advise stay in Tawau and make daytrip to Semporna.
