‘I am tired from today’s strenuous activities and want to go to sleep.’
Down to the skeleton sentence: ‘I am and want.’
In this case, the verbs (am, want) share the subject (I), and when that is the case, there is NO comma. So:
If two verbs share the subject -> no comma
And not only that but the sentence also lists two actions about the subject:
want to go to sleep
When there is a listing of only two items or actions -> no comma
Tip: If you’re new to all this, use the ‘Find’ function in your word processing program for the word and when you’re done with your chapter. Read each sentence that contains and. If each verb has a subject, add a comma before and. If two verbs share the subject, make sure there is NO comma. This way, you’ll probably have eliminated a good 50% of your error count.