A theme party is like a caricature. You take an aspect of a culture and overemphasis it. When you are doing a Mexican theme, think vibrant and vivacious. The colors should be bright, loud and excessive. The music should be upbeat and fun.

Decorations
Primary colors or red, green and white.

Streamers are a must. Decorate the room with lots and lots of colorful streamers. The colors and sheer amount of the paper streamers should be vibrant and overstated.

Decorate the room with colorful, oversized paper flowers too. Make smaller flowers for the female guests to wear in their hair.

Paper flowers
To make paper flowers you will need 6 to 10 pieces of colorful tissue paper (the bigger the tissue paper the bigger the flower) and long pipe cleaners.

Lay the tissue paper out on a flat surface. Place alternating colors one atop another, keeping the stack even.

Starting at the left edge of the stack of tissue paper, begin folding it accordion style, first forward, then backward, as if you were making a paper fan for a child.

Secure the folded stack tightly by twisting one end of the pipe cleaner around the center of the stack. Leave the length of the pipe cleaner long and straight as it will serve as the stem.

Gently pull the first layer of the folded tissue paper fan toward the center, first the left side, then the right. When you have fanned half of the stack, flip it over and continue to pull toward the center until you have a round flower.

Piñatas
A piñata placed in the center of the room adds a nice touch and doubles as a game at the end of the party. Commercial piñatas now come in a variety of styles, like chili peppers or cacti.