This one is simple. Keyboards need a key that means “swap the characters on either side of the cursor”. I type words like “htis” all too often, and I suspect I’m not alone. Instead of positioning the cursor, deleting a letter, moving the cursor, and re-typing the letter, how about positioning the cursor between the offending letters and pressing “Swap”. While we’re at it, make variations such as Control-Swap to switch the two letters immediately behind the cursor, and Alt-Swap to exchange the two letters at the beginning of the latest word.
Now there’s something I could use. A lot.