There's really no way of actually making yourself sick unless you eat some bad food which I don't recommend or you get around someone that has the flu etc.
Then if you're around a friend or family member that has the flu then you can become sick with the flu which is not very fun.
You can try faking sick though to get out of school by waking up earlier than your parents and go to the bathroom and act like you're vomiting into the toilet and be sure to make loud noises.
Also you can fake a fever by placing a hot towel on your forehead and running hot water over a thermometer to raise the temperature of the thermometer.
Also be reluctant to get dressed when your parents want you to go to school.