`Ctrl + v` to visually select one character at a time (instead of say `Shift + v` that selects a whole line) and then use the movement keys to select a block of characters horizontally as well as vertically. Imagine several well indented HTML <li class="something"> elements, you could for instance delete/modify all the class attributes on all lines visually in one go (to insert text use `Shift + i`, type, then Esc).