Brake hard on smoother pavement or cement
A smoother roadbed will have a better surface for you tires to slide across and in order to grab and release repeatedly to make the sound you are looking for.
Tires squeal when they are grabbing the road surface and letting go thousands, if not more, times a second. The vibrating tire emits the sound as it goes through the process.
As well, you might have anti-lock brakes which prevent a good squeal from occurring.
You can try:
Disabling your anti-lock brakes
Softer tire compound for more friction
Making sure there's no gravel or dirt on the road you want to squeal on
As well, you can carry a broom with you to clean road surfaces before you drive on them to make sure you can get a good screach when you lock up your brakes. I think a great surface would be large cement slabs joined together with smooth concrete, just like a gas station or even the inside of a shopping mall (you'll want to get permission from the property owner I would think).
Good luck making noise with your tires and may they be as obnoxious and loud as you hope for!