Hi. I had the same problem before and I realized one thing. HTML+TAB It doesn't work if you haven't saved your file yet in my case as .html. Of course you're creating a new html document, it make sense that you haven't saved it yet until you've type few codes. But sublime text may not recognized what type of file you're creating yet and so it's not sure if html+tab is applicable. But as soon as you saved it to .html, then html+tab will work. No need to do changes in settings.
Hope this helps.