Steps for Negative Tú Commands:
1.) Take the 1st person singular version of the verb (yo form).
2.) Drop the "-o"
3.) If it's an -AR verb, add "-es". If it's an -ER or -IR verb, add "-as".
3.) Don't forget to put "no" before the verb.
Examples of Negative Tú Commands:
-To conjugate the verb correr into a negative tú command you conjugate the verb into the yo form, which would be corro. Then, you drop the -o. Since it is an -ER verb, you add "-as" to the end, which would make it corras. Make sure you don't forget to add the "no" before the verb! No corras. Which means "Don't run."
-To conjugate the verb participar into a negative tú command you conjugate the verb into the yo form, which would be participo. Then, you drop the -o. Since it is an -AR verb, you add "-es" to the end, which would make it participes. Then add the "no" before it. No participes. Which means, "Don't participate."