Use the Shift key on the opposite hand from the letter you're typing: right Shift for left-hand letters, left Shift for right-hand letters. Then add the punctuation you'll use in every sentence.
Hold right Shift with your right pinky, type the letter with your left hand, then release.
Hold left Shift with your left pinky and type the capital with your right hand.
A period ends a sentence and is followed by one space. Commas go straight after a word.
The apostrophe and quote share a key next to the semicolon. Use your right pinky; add left Shift for double quotes.
The question mark is Shift + slash (right pinky, left Shift). The exclamation mark is Shift + 1.