How to select a HTML tag

There is no special shortcut to select a tag. HE generic editor, and not specified for any language (this would change with 1.50, where specialization will come with the help of plugins and scripts).

But you can use command Edit.ExpandSelection (Edit→Selection→Expand). This is a smart function that guesses, what user want to select and increase selection range from current to a larger one. The functionality is also callable with double/triple etc clicks (number of clicks corresponding to the number of calls for ExpandSelection).

The opposite to Edit.ExpandSelection is command Edit.ShrinkSelection, which decrease selection to previous selection scope.